I had a similar misfortune. I loaned my first uke, my beater, to my girlfriends brother for a while. It was great when I got it back, just havinga uke I could keep at hand again, not worring if it got knocked or banged. Anyway, I decided one day to write how much I loved my girlfriend on it in biro, thinking what a nice thing it was to do. Anyway, I thought it would rub off but it didn't. It's not such a problem as I was gonna paint it anyway, but I thought it was such a nice thing to do I didn't mind it being there. So much so it'd actually be a shame to paint it now. Then again, it's a huge contrast between a cheapie beater and a new Kamaka. Just thought I'd share!...
If all else fails, with him being an artist maybe he could put some design on it!? Atleast he'll have a unique uke and you never know, it may just look awesome!?...