Takes a bit of time but maybe write down the contacts?

If not there may be an app someone else would know of here or you might be able to go in-store and get them to do the backup before you reset everything on that little machine they have

 

Hit menu while looking at contacts, export the contacts you have. Remove his account. Add yours, then open contacts, and import to your account. sorry I cant be more specific, but its late....

 

Yes basically you are going to backup the contacts, Google Calendar entries and any Gmail messages as they are tied to his gmail account. Export the contacts to a file on the sdcard and then remove his account. I have heard that you can only remove the ownership gmail by doing a factory reset, but I would try to just delete it first. Once that is done, log in with YOUR Gmail account and then import your contacts and whatever else you need. You will need to reinstall any apps you have, so jot them down as well before deleting his Gmail.

Good luck!

 

*still doing the Bear dance*