Sex Issue

So during sex my bf has me ride him and that's my least favorite position. I want to tell him to just fucking bend me over and pound me from behind or fuck me in the ass (he's never done the latter of the two but has done the first when we were first together) but I'm too much of a shy little bitch to actually tell him. I'm a total sub so I can't bring myself to say no to him. How do I get what I want without being upfront?