If you are going to have to cut anyway, I wouldn't do the grommet. I'd just used the method where you cut a slit in the back of the WSM along the lid.
http://www.virtualweberbullet.com/cutting-a-probe-thermometer-slot.html
I'd feel way better doing this than I would trying to drill a hole for the grommet. Mine came with the grommet so I just use it, but the slot is probably more convenient. If you feel comfortable with it, then go for it.
Yeah, I've seen that mod also. I am torn, that does look to be easier to use, but I also kind of like the "stock look" of the gasket. I don't think it would be that bad to drill for the gasket with a step bit, no?