Any tips/hacks for friend with injured foot?

What does the MD say? If he hasn't seen a doctor, he should, and follow instructions. You can then adjust your itinerary and level of activity accordingly.
I sprained one ankle on a trip and broke a foot on another trip. I sat out a lot of activities both times.

Would a walking boot with soft inserts help? No matter, he'll be shifting weight onto different muscles and bones, which creates different problems.
There's no quick fix.

What do his doctors suggest? A specialist?

Hiking/walking poles to help ease pressure. Need to go in a checked bag or be used as a mobility aid through the airport security.

See a podiatrist. A really good one. I am in Greece now and the second one I saw taught me to tape my toe and my foot. I have done serious hiking with the tape, metal insert in hiking shoes and new orthotics (recommended by first podiatrist). My problem is different than his so don’t want to generalize but he should do what he can to see someone really good.

Also, I brought a hot water bottle and have filled it with ice and iced my foot. I figured out I could freeze it in the freezer which was much easier than putting the little ice cubes the freezers have had. The bonus is I have used it to keep drinks/food cold while out and about. Thus, the next piece of advice I would give you is to have a fridge.

Finally, look carefully at shoes. I have some SAS sandals I happily wore in Italy last summer but figured out a few weeks before we left that they made my feet ache. I ordered some ASTREX ones with built in support through Amazon (only way could get fast enough) in two different sizes only a few days before I left. They are a dream. I can walk reasonably far in them and more importantly give my feet a rest. I wear them around hotel rooms because I absolutely cannot go barefoot. I also took hiking shoes and sneakers. Even before this, I have had problematic feet and must change shoes. You can always take fewer clothes and wash more frequently. Don’t skimp on shoes.

I'd suggest a chat with a doctor or a foot doctor and do what that say...

...and quickly!

we're due to leave for Greece in a week and a half!

Orthodics and other built-for-you customized gear often takes a lot longer than that. Heck, these days just getting a doctor appointment can take weeks. Giddyup.

My orthotics, while recommended by the podiatrist, are not custom. I ordered what she told me to get through Amazon.

Had to research what the condition is. ( https://my.clevelandclinic.org/health/diseases/21671-sesamoiditis )

Depending on how severe and the cause the treatment measures and time to recover can be a few days to months

Communication with the health care provider is the real answer.

I agree that seeing the specialist is the best first option. Don't know if that is possible at this point; if it is, a steroid injection might be helpful based on the article linked above. I have arthritis in the largest joint of my big toe. I had custom orthotics made, but can't seem to get them to fit my shoes. My doc said the most important thing for me was to immobilize the joint when I walk, and that carbon fiber insoles might be more effective for me, since they're fairly thin. That being said, walking uphill is the worst, as it flexes most the entire area you're talking about, and should be minimized if possible. I've found that one of the best ways to ice and gently stretch my foot is to freeze a water bottle and roll it back and forth. The contour just seems to fit and it is a fairly easy transport. Wish him all the best!

I concur with joe32f- “communicate with a health care provider.” BTW excellent article that Joe referenced. As a triage nurse for many years, I too would strongly suggest consulting a provider.

I have a similar condition and just got some Teva sandals that are working really well for me: stiff bottom, almost like a walking boot; adjustable velcro strap around big toe joint; soft, cushioned insole; and wide heel, for stability. Plus they're water resistant.

He can order from Zappos (get a couple of sizes -- I ended up with a half-size smaller than my normal shoe). Free shipping, free returns.

I'm not sure you can get these before you go, but I use the MELT Method balls from Sue Hitzman for plantar fasciitis which I realize is different than Sesamoiditis. HOWEVER, I'd get the hand and foot kit to start rehydrating the fascia and see if that helps with some pain relief and mobility.

www.meltmethod.com

I have no connection to this company other than being a satisfied customer. For myself, it relieves foot pain and helps to make my feet be not so tired after a full day of tromping around a European city (or a geyser basin in Yellowstone which is where I'll take them next, lol!!)

Thanks all -- he saw a physiotherapist yesterday. Definitely taking suggestions on Tevas and other things to make it a bit easier on him.