To clarify, the current pass is a fixed block of AAirpass miles that have to be used in a year. You can roll them forward to the next year if you renew the pass. I think the smallest one is around 25k miles at .40/mile base or $10,000.

If you just want to spend now and fly later- you could also just buy Aa gift cards. No expiry on those. Maybe they'll give you a discount for a bulk purchase.

I'm assuming you've already maxed out any retirement options like a SEP Ira or solo 401(k) for the deduction.

You might also look at United. I think they have a prepaid product (or at least used to) that works as you suggest. Pay up front then dollar amounts get deducted as you fly, with discounts over regular revenue fares. Pass Plus?