Does anyone know if you can get a tollroad payment option with rental cars?

Here's the web site for the French telepeage outfit. Last time I checked I believe there was no way to get it until you're in France. https://www.telepeagepourtous.fr/fr/particulier/toutes_nos_offres/formule_balade

As to car rental agencies, I seem to remember seeing some info about that, but it seemed prohibitively expensive.

There are various companies offering tollroad payment schemes. However, I am not aware of a single option that is available for someone who does not have an EU bank account. You can always ask.

We have one that we bring with us, that we got many years ago at the office of a large toll plaza leaving Paris. It's tied to a cc and is automatically billed. I don't remember if they asked for our Fr bank info. It works on all French autoroutes. You use the lanes on the left with "t".