Do iguanas have a gag reflex ?
Try feeding him and he won't constantly be hungry. He's biting your fingers because he's HUNGRY! If you're thinking in terms of trying to gag your pet, you are an abuser and should rehome the iguana if you aren't able to properly care for it.
Figure out why he is biting.
Don't have your hand get close to the iguanas. Use a grabber tool instead.