Urge to pop fingers

I’m trying to stop popping my fingers, which has been a habit for many years. I tried doing a Model on it, but I can’t identify a thought that happens right before I pop my fingers. I think its just a compulsive subconscious habit. I do know I pop them more often when I’m nervous about work, and I’m sitting at my desk. Here is my incomplete model:

C- working at my desk
T – ?
F – nervous
A – pop fingers
R- reinforce urge to pop fingers when sitting at my desk working

Any ideas as to how I can finally stop popping my fingers even if I can’t identify a thought? The bigger picture question is how can I use the model with a compulsive urge where the thought is not apparent? thank you.