I'm sure they would accept a large upfront payment. But if they bill you each time you use a return you won't be able to wait months to pay it all. They'll sic the collection dogs on you.

Are you wanting to get away from the Pay per Return option for an unlimited program?   You would need to call customer service.

If you want to prepay your Pay per Return fees for 2022....be careful.  I don't think your balance, if you pay through the 2021 program, can be carried to 2022.