Tell him to go for it. People may talk about it not being "quality time" or "not counting" or "blah blah blah". Fact of the matter is, multi time is multi time. He wants to go putt around in a 337 more power to him and I doubt any airlines will say "Gee, it's centerline thrust...you must have no idea what you're doing." I'm sure when he loses the engine on his sim ride during the interview, they'll figure out if he knows what he's doing....

...unless he goes to XJet...then they'll just find out in training