i spent the good part of the last year teaching my current boy he has to mount to get off. he did a similar thing to yours, sort of stand behind me and hump the air. or just plant his sheath in my hand/face for me to do all the work.
he really hates having his front legs lifted, maybe some bad experience from his youth. i don't know. i couldn't just lift him on my back and jerk him for him to understand mounting is okay. i just had to get a bit creative.
i started with us on the ground, me sitting to face him and just jerking him off as he humped the air. leaning into him a bit, trying to get him to connect the dots of "if i'm propped against him, pleasure happens". i jerked him until he fully engorged and didn't let go. simulating a tie, just with my hand. he'd either chill with his head on my shoulder or turn around to let me suck him too.
we did just this daily or every other day, dependent on his mood, for maybe a month.
one day i added putting one of his front legs on my shoulder as i jerked him during the sessions, he didn't mind having just one of his legs lifted as he humped into my hand. after a few sessions, it resulted in him signaling what he'd like me to do by putting his paw on my shoulder on his own.
after some sessions of doing just that, i tried what happens if i jerk him just for a bit and let go. he got frustrated for a bit, wanting to get off, nudging at my hand. i just sat still and did nothing. he then jumped up on my shoulders with both legs on his own, i grabbed his penis to continue jerking. let go if he jumped down as many times as he needed to understand that his legs on my shoulders are a good thing (i think he was taught not to jump on ppl before i adopted him). i used no words or sounds during that as i wasn't trying to teach him commands. i did praise him after each session. he still hates having his legs lifted, he either puts his legs where he wants or nothing happens.
this turned our session into frontal mounting for quite some time. i also learned i kinda hate getting face fucked during that time.
it was kinda simple to one day change our "thing" into him mounting me properly. he knew grabbing me is okay and i knew he hates being lifted so i did the jerk for a bit and let go and let him figure out what to do next to get off. he jumped up on my shoulders, i jerked him a bit and let go. he jumped down and tried to front mount again. i turned around and presented my backside and he in his unfulfilled frustration grabbed me by the hips and pounded away.... he needed a lot of guidance by my hand at first to hit the mark. now all i have to do is take my clothes off and get on all fours, if he's interested he mounts.
