1. Cumming in or on something and then licking it up afterward. This one seems the hardest to me. After an orgasm I just don't have it in me to do it. The only way I can think of doing it assuming I wasn't tied up is with force or blackmail. The force part of it would have to be something like having the shocking dog collar locked on my balls. I would be shocked if I didn't eat my cum up willingly. The other is being threatened with being outed in some way.
2. Being tied down and forced. One way is for Mistress to fill her pussy up with my cum and sit on my face. We use lube so that’s not a good solution. I recently put a container of coconut oil in our toy drawer. Apparently it’s the latest and greatest lube. My only fear is our coconut oil is pleasantly flavored. Ideally she would sit on my face, au naturel. Knowing how my libido drops after an orgasm I imagine Mistress would need to grab my balls in her fist and threaten a squeeze if I didn’t comply.
3. Saved cum. This one is different as Mistress would have me save my cum up in a container we could keep frozen. At some point she would tie me to the bed and put this frozen cum in my mouth. The most devious plan I've heard was that a Mistress put the frozen cum in her slaves mouth and duct tapes it shut. She immediately gives him an orgasm, his libido drops through the floor, and the cum has barely started to thaw. In turn he is forced to endure the slow thaw of his cum, dripping down his throat until it’s all gone. In my mind I am debating between being blindfolded or not. Watching the cum cube drop in my mouth would be terrible, but not knowing what is coming until it’s too late is also a mind fuck.
4. Cum conditioning. I read a blog where the man was tied up and fed his cum every day for a couple weeks. After that amount of time he had no qualms about it and then cleaned it up every time no matter where it was.
http://lazydomme.blogspot.com/2011/05/forced-cum-eating.html (the comments here are very interesting)