I first tried this with my ex a few years back, and recently got my current wife to go in for it without much convincing...

If you find yourself watching her with a guy what you do is have her lie on her back or on all fours and suck his cock. As the cuck you aren't allowed to touch her but you are instructed to jerk off on her pussy or ass as many times as you can while she sucks him. Try to see how many pathetic loads you can produce on her before he can reach his first orgasm...My record so far is only 3 loads in about 45 minutes but I think(hope!) it can be beaten.
Obviously for some advanced couples this game may not apply because the husband isn't allowed that close to her pussy while she is serving her lover or maybe not at all...but still I just wanted to share it because we have found it to be VERY much fun. Cleanup is usually the second part of the activity of course!