Better idea ... he needs to send out a petition to the American people and forward to Congress those petitions to build the wall. Along with that petition, people could send in a donation AND the President could also challenge big Pharma, corporations, etc., to match his donation (perhaps a million).
He had roughly 63,000,000 votes in '16. Approximately $80.00 from each of those people would give him the $5 Billion needed. IF Congress would be willing to honor the petition and allow those donations to fund the wall, I am absolutely certain, he'd get well over the funds needed. We'd have our wall. The middle finger salute needs to be given to Congress on this. We ARE the government. They work for US, we don't work for them!