I heard back from tech support this morning. They recommend drilling out the rivets, cleaning it up, and redoing it with fuel tank sealant. It'll be a pain, but I agree with them.
So now I need to order some sealant. Proseal at Aircraft Spruce is tres expensive, $78 for the smallest quantity, but it turns out Vans has it, or a newer incarnation of it, in 3.5 oz quantities for around $16. Horray for Vans!
I'm still working out how to clean the epoxy off the aluminum parts.