Ok, I only skimmed through the responses, and I realize this was started a long time ago. I might be repeating what others have said. I don't know. I don't even know if the creator is still on EF, or cares. But.. here's my take:

COMMUNICATION! For any and all fantasies with anyone else, the first and foremost issue should be communication. You and your partners) need to talk about these fantasies.. extensively.

For a fantasy to be followed through and actually happen, both partners need to at least be interested and willing. If, to either person, any fantasy is too weird, gross, abnormal, or whatever.. then you need to understand why, and maybe explain why you are interested in it.

Then there's the reality. It's completely different to talk about a what-if situation, and how-about situation. You need to talk about the realities of it. Brainstorm together! Come up with ways, means, rules, lines to draw, and all the details you can think of.

After lots and lots of talking the subject to death, if both people (assuming it's two people involved here) agree and are still interested and both people still want to do it, then. .it can happen!

Of course, safety issues should always be talked about, and strict rules/lines should be drawn. And during, keep the communication open. After all, you're in this together!