This mythical back up pg just doesn't exist or isn't coming to SLU.
If he would be satisfied with just being the back up pg and that's it, he isn't going to make a difference when Yuri is out anyway. Sorry, he just won't be good enough.
Otherwise he needs to be good enough to take wing/guard minutes from Perk, GJim, Pick, Thatch, Parker, Hargrove, etc ... Players that good have other situations available to them that offer them more assurances for playing time.