I don't think its possible without years of therapy. Defense mechanisms are unconscious. Therefore you cannot manipulate them when they arise. I have a few conscious ones that I also use, that do the trick. Like right now, it feels like acid is leeching out of my heart and through my pores for absolutely no reason whatsoever. Its not very nice, is unnecessary and irritating. So I do a few swallowing motions and say to myself in my mind "suck it downnnn!" (its a line from a video game i used to play, lol) and bam... feelings gone. But other defense mechanisms I do without knowing, and they are so good that I don't even notice I had a feeling in the first place. Problem solved.

I know that if i just let myself feel these unnecessary emotions for 5 seconds, there would be dead people on my street. Dead people leads to jail, and then we all know what happens after that. Its called harm minimization. And all for what? I would have gone to jail for no reason. Why go to jail when you can just use your coping mechanisms to your advantage?