Yes, just use your computer to JB don't sync and all he has to do is hook it up to his computer and right click on the phone in the left column of iTunes and choose restore from backup. This is only settings and data it has nothing to do with the OS so no the restore wont remove the JB. What method are you using to JB? if it's Pwnage Tool or Sn0wbreeze then make sure your friend does a backup and a sync before you start.