You can create the new sims/pets and then import the ones you want from My Studio then delete the ones you had to create for the new game. I think you press triangle while they're selected and confirm the deletion. Do this while you're still in create a sim..don't begin the new game til you've sorted the sims, obviously.
My partner figured that one out lol. Anyway, best of luck and I hope this is the last game you'll have to start over with..I guess you've gotta take it in your stride on the PS3 version, don't you?