When I first started, I went to the local shop and tried out a ton of basses. I didn't really know any songs or fancy riffs or anything, and there were few people already auditioning instruments through the amps. (Talk about stage fright!) So I tried everything unplugged. Once I found a couple that felt good and an amp opened up, I just played some quick scales, intervals, arpeggios, etc. at low volume on each bass while fiddling with bass EQ knobs, etc. to sample the sounds of the different instruments.
Knowing now that most combo amps have headphone jacks, I suppose I could have done that. It would have been significantly less intimidating! I could have used the excuse that I wanted to hear the instruments without all the background noise. So that's my idea for your friend. And if he doesn't already have good headphones, the local music stores will probably have some decent demo headphones over in the keyboard section. He can ask a clerk if to borrow a set for a few minutes. Also - see if he'll during normal work/school hours. The store will probably be much less busy.
As for what bass to get him if he's absolutely against going to the store... No idea. I'd guess a P since that's what he used to play. It'd probably feel the most familiar to him. Honestly though, I wouldn't want someone else to select an instrument for me.