Pretty strong odds that you are aiming to lose both money *and* a friendship. If you are the sort of fellow who has trouble saying no, just offer your friend a gift of whatever amount makes you feel comfortable. Or least uncomfortable. Maybe $500, maybe $1000. Not more. IOW, skip the loan idea altogether and gift him a small amount of money.
If he values your friendship as much as you value his, he really should be touched by the offer but turn you down. Or you could raise this uncomfortable issue in front of his wife, and see what she says.
If he values your friendship as much as you value his, he really should be touched by the offer but turn you down. Or you could raise this uncomfortable issue in front of his wife, and see what she says.