I'm usually more comfortable on my back... and make sure he's turned on and well lubed. For me, the closer I get to cumming the easier it is to put things in my backdoor. Go with Diva's suggestion... start licking and sucking his cock, then start to ease a finger into him. Sounds like he's willing so he'll probably enjoy it. Good luck.

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Put me on wheels and I'll turn tricks.

Clever? Nah, I ran out of that years ago. But if you find this, let me know, k?
"The road goes ever on..." ~ Tolkien

In memory of my friend skip...
Go then, there are other worlds than these