You'd have to do it as Earnest Money to the contract, though. The money would sit more than a day because of how long the mortgage process is, so you'd lose it all before you could use it for the down payment.

Earnest Money, however, is paid as a contingency to the purchase agreement must be held by title or cashed by the seller. So you'd have to get someone to agree to sell you a parcel same-day, get a contract written up, and probably best to transfer the earnest money to title for holding. $20k spent right there.

The biggest issue with it, though, is any company or bank willing to give you a mortgage are really going to want to know how you came into $20k in cash, and that's going to be more or less impossible to accomplish.