An idea I had recently for a straight to gay conditioning file;
The idea was that the gesture of putting one's finger in a hole made by the other hand would cause the subject's cock to feel like it is thrusting into an asshole and condition the subject to enjoy topping alongside suggestions of pleasure, arousal and a growing urge to go find.
An alternate version could also cause the subject to feel a cock entering their asshole instead when triggered by the gesture could also be made for bottom conditioning.