As far as "dumb as the bank thinks" they only looking back so many months for statements. So if it was there the whole time, they won't see how long it's been there. You can call it a gift and transfer it without any tax implications but that will go against your lifetime gift value.

Whoever does it has a lot of risk of not getting it back, so theyre the real dumb one here.

In 3 months the business he wants might be sold already.