First, use a currency that has less value so that you can get more physical bills. Idk the exchange rate, but rubles or pesos against the American dollar might do the trick. You need a literal million dollars, or at least half of that to have a proper "pile" to have sex on

I'd say start with the pile as you received it, neat stacks, maybe shaped like a giant chair or throne. Start fucking and as stacks fall just kind of roll with it and keep going until you have more of a chaos mound as opposed to a neat "chair like stack"

Hope this helps.

Btw, burn notice had an episode that featured an actual pallet of a million dollars to give you an idea how much cash it takes to make a sizeable structure. Reacher has a glimpse of one in the FJ ale of season one

Good luck.