It can't update automatically. Your mate may have restored his game save, due to whatever, so it won't match or be an accumulation to what it was (hope that makes sense).That's why they have to logon and choose "recieve" and update their Bobs in this way.
Even newbie Bob's are gaining so much considering the owners zero amount of input. Whether they come last, or mid-field, they are still gaining a more than decent amount of cr/xp. Your mate could check in a week and his level 0 Bob will jump to 5 or more.
Myself, I don't care if my Bob's come last, as long as they're getting used to help me gain credits. I've been hosting a lot of races, yet getting very little in return. eg. I've pushed 5 blokes Bobs to all over 3 "price lights" (+200K) so I hope in the next week they do me half the favor. If your online friends don't do ANY hosting, I wouldn't worry about the xp or giving them free money.