It's tough to build the association. First you have to make sure the dog's need are met physically and psychologically. He won't consider sex until he isn't hungry, thirsty, in need of exercise, etc. You would need to have spent weeks or months getting him to trust you.
Next steps are subjective and different people have different approaches. Next you can establish yourself as a submissive playmate. Play with with him, mouth play and toys, and let him to whatever he wants. Play a lot while on the floor at his level or on your back laying down. Allow him to do whatever he wants. Mouthing on you, licking, whatever. The point is to build his confidence and understanding that your the person to try things with. Your his bitch. Mounting is a big no-no if he thinks your too dominant to accept it.
You can then start rubbing his sheath to get him a bit horny. But don't expect anything - he does not view you as a solution for that yet. Eventually he may take a small step in the right direction. Rearing up and putting his paws on your back, for example. Totally random. Praise him highly. Try to get him to repeat the behavior without forcing it or trying too hard. Then maybe he'll get a bit closer, actually grabbing your back, but just in play. Now he thinks on your back is the cool place to be. Things progress from there until he eventually is mounting. When he mounts try to be very stable and push your butt into his penis as he does it.
So if you're wondering if there a way to just trigger his natural instinct and make it happen all at once the answer is very likely no unless you get very lucky. Most dogs I've gotten had no idea what to do until I went through the steps above.
One time I went to a breeder and paid him to give me the smell of his dogs in heat rubbed on paper towels. I said I was doing guard dog protection training and I need training aids to teach the dogs not to get distracted. Your milage may vary by trying that. Even though having that scent around would help a lot it is actually still not a magic solution because making the dog horny won't just make him come up with a new idea he's never had before (humping you). But if you do get dog in heat scent it can help the training described above a lot. Good luck!
