The first signature on there by the person who purchased them has to match the signature at the time of purchase so I would say no. Unless you had him sign some at purchase, which he could sign when spending, he can't sign them.
This is the first year I am not taking some money in TC's. They are easy to use onsite but the CM's are VERY careful about checking everything is correct. They check ID, and they always check the signatures when I've used them. I wouldn't risk it