Disclaimer: As it is right now, this mod is all about improving feel. Aesthetics will be worked out later. 
Long title... lol.
As some of you know, I recently installed the B&M short shifter in my Z. It's awesome, I love it, and yes, I trashed the factory shift knob during the install.
One of the big problems with short shifters and an aftermarket knob is the boot. Often times the boot is going to be too big for the new shifter and knob. Our factory boot is obviously designed to accommodate the fairly wide base of the factory knob, so this is what it first looked like when I put my aftermarket Team Voodoo knob on:
Kind of sloppy, eh?
Not to mention the feel of the boot freely slopping about...
Looking for a temporary fix I made a trip to Lowe's. I picked up a number of black rubber grommets and a 5/8 x 7/8 x 1" steel spacer.
I ended up fitting one of the larger grommets around the base of the spacer and slipped it over the shifter, then tightened the knob down as far as I could go. The knob obviously sits a little bit higher now (about 3/4" higher than before), but the end result is a better looking and better feeling shifter.
The finishes don't match but I might be able to find a spacer to better match which I would then spray with clear like the Voodoo knob. I might just paint this one silver and clear it... or just leave it as is.
Here's a shot with levels adjusted to show the grommet better...
So that's my temporary (possibly permanent) fix. Hope this is helpful for anyone in a similar predicament.