I often have the same feelings. What I do is tell myself I can but first I'm going to do this. And then I go do what ever it was I needed to do like watch a movie or do house work or reply to an email or forum or anything. Then when I finish that, if I still want to harm then I do it again. I tell myself that I will let myself harm but first I have to do this. And eventually I can get past the urge. I allow myself to have that fantacy of being able to harm without actually doing it. It helps take away some of the anxiety of trying not to harm.

I don't know if what I said maked any sense but that is just something I use sometimes. It does not work all the time but it's worth a try