Car Rental

The last places on earth you want/need a car are Zurich and Venice. You can easily take the train from Zurich all the way to Venice and not have to deal with rental car headaches - foreign drop charges being only a part of the headache.

There's a direct train from Zurich Main Station all the way to Venice S, Lucia in only 6.5 hours. But of course you should hop on the train to the Lauterbrunnen Valley first and experience the stunning Swiss Alps before heading off to Venice.

The fee is not for a different location drop-off, it’s for a different country drop-off. I don’t think there is any way to avoid it except by not renting a car. Why not look into trains? Or, find the Swiss city closest to Italy where you can drop the car and train from there. The lakes area is very attractive, and Venice can be reached easily from there.

The drop off fee is to pay for someone to physically drive the car back to Switzerland, and you cannot get around it.
With so many days before your tour, you could take a train through the Tirolean Alps from Zurich to Innsbruck and spend the night(s). Then catch a train in Innsbruck, go through the Brenner Pass to Verona where you'll connect to a train to Padua.
Or, you could catch a flight from Zurich to Marco Polo Airport in Venice. You could rent a car there and take in sights you're not going to see on your tour.

a Rick Steves back country Italy tour

Presumably you mean the "Village Italy" tour?

Rental car issue solution: a) do not rent a car; b) drop car in same country as rented

The drop off fee can’t be gotten around. Why don’t you take those 3 days you had planned to drive and pick a 2-3 night stop between Zürich and Venice, traveling on the excellent train system? There would be a number of great choices.

Tim has it nailed. Do the trains with a couple days in the Lauterbrunnen valley.

We are flying into Zurich and spending three days driving to Venice and three days in Venice before joining the tour.

If I am reading this correctly you have 6 days between the time you arrive in Zurich and the time you need to be in Padua.

Here is an option to renting a car. After arriving in Zurich, take a train from Zurich to Chur (1.5 hour) and spend the day and night recovering from your flight in Chur. The next day take the Bernia Express Scenic Train from Chur to Tirano (4 hours). Spend the night in Tirano. The next day you can train from Tirano to Venice via Milan (5.5 hrs.) or if you like to break up the trip, spend a night in Milan and train to Venice (2.5 hrs.) the next day. This will leave you 3 nights for Venice.

I'm sure at first glance many might think one night stays are taboo, but if you drive towards Venice from Zurich, you will have one night stays as well. Plus, depending on your driving route, it can be 350-415 miles of driving. The driver always loses out because of paying attention to driving and driving fatigue. The trains are the way to go IMO. Enjoy your tour and trip.

It’s just so difficult for some travelers (mostly Americans) to understand that a rental vehicle is not always needed or wanted. In the USA there are no other choices so naturally that’s just our knee-jerk reaction.

I assume that your plane reservations have been finalized, but if not, you could fly into Venice, then train or cheap internal flight round trip to Zurich.
We are also doing the Village Trip this April and many on the travel form for this trip have suggested sending some prior trip days in Padua.