This idea isn't entirely knew, there are some excerise or punishment files.
I wrote a script for running a mile or sucking a cock. Gender nutral.
I took the mile as the assignment and the cock as a punishment.
I thought of adapting it to any oral sex for the punishment but decided finding a girl give oral sex too would be difficult so I made it just about finding a guy so there's no, I couldn't find a girl excuse.
Also it has to be a new cock, making it more challenging. The file ended up being fairly empowering actually. The idea is that you will make yourself run (and maybe suck a few over time?)
Should I post the whole thing? I'd be interested in suggestions.