Well, just did this mod, ground about 0.20" off each of the four bushings. Let me begin by saying thanks to the OP for this idea.
First thing I realized after doing this was "wow, people actually pay ~$40 for those bushings?" I totally misunderstood the point of the bushings until this mod. I had thought they were somehow replacing something in the shifter cup.
Second thing I realized is that while this is a great idea to save yourself the ~$40 for the bushings, it is by no means the night/day difference that people made the TWM bushings out to be. I'm 100% certain that this mod accomplishes 99%-100% the same thing as the TWM bushings. If someone else had done either mod without me knowing it, I don't think I'd be able to tell the difference, other than it is a slight bit "noisier" now when shifting. I'm sure my MM had a lot to do with that, though. I'd be PISSED if I spent $40 for the bushings, which I almost did.
Third, I think the counterweight remove idea had much more of an effect (for better or worse) on shifter than this does. I tried the counterweight removal, but preferred it back on. I think people might want to consider trying this free mod as well, as it is completely reversable, and might compliment this mod well.
Again, I am in no way trying to s*** on your idea. It is great idea and great way to save people money. Greatly appreciated.