I have tried something similar, but was not as serious about it at the time. Ultimately, I used the softness of the goal as a way to step away from it more and more each day. What I have considered is to choose a couple smaller sub-goals within the theme that I want to work toward so that I still have a bit more concrete of a target.
Interesting, I have thought a bit about that as well, having daily/weekly micro-goals instead of one huge goal should make it work.