FWIW, I found several possibilities. One place with 2 "downtown" San Francisco locations will rent Priuses. I'd probably need to take BART there if I flew into SFO, or took the train into Emeryville.

Another possibility is Toyota dealers with car rental programs. One is practically adjacent to SJC. There's also one I could probably get a cab to from Emeryville.

So I need to finalize my plans and then figure this out.