Finishing Him Off

So I'm having a problem getting my boyfriend to finish while I'm giving him head- I know that it feels good while I'm giving it to him I just think my problem is he wants it to go deeper down my throat which, sadly, I'm not one of those girls who don't have a gag reflex. So it's a little harder for me to do. I know I need to go fast and deeper, but are there any other tricks I can use that don't involve his rectum or anything like that? Something I can do with my mouth tongue hand, anything! Because I know I end up worrying about my teeth. Someone help me out here!!