Blackie, If he does not want sex, he will not let me touch him, hard or not.
So your idea, while tantalizing, would only work on the nights when he already wanted it.
NOP's idea of placing his hand on ME is really intelligent. I am too distracted at the moment to figure out why this is less threatening--and delve into MrH's thought process--but it is much more successful than chasing him around the bed trying to touch him. And I'm talking about regular ol' touch.
When he doesn't want sex (even though he's hard) he seems to not want to be touched anywhere, lest it lead to nookie.
Howeverrrr, I will give ya this: Many times when he doesn't want sex, I have been able to 'talk him into it' by snuggling up against his hard on and pretending to go to sleep. So your method is close to being operational on an LDH but not quite there yet.