Yeah I've had my share of cock-blockers in my lucid sex dreams as well.

One that used to be recurring, was when I tried to have sex with the dream version of my boyfriend while I was lucid. He would turn into a demon, and bite my hand. Hard. It wouldn't wake me up thankfully, but I was getting sick and tired of repeating this dream, since there were so many more fun lucid things I could be doing instead. But I was bent on conquering it, and I finally did. But only after talking it over with a friend in real life, and working out a plan that focused on my lucid strengths.

All in all, I would say that I rarely have control over the behavior of my DCs. They are what they are, and do what they do, and I just go with it or fight it. I eventually win either way, but it can be frustrating when I'm trying to get off