I've been using Joe's idea from his Savoia Arcade site & it has worked well.
http://www.geocities.com/gijoekerr/It consists of using a Dremel with a guide attachment & a carbide cutting wheel.
The wheel cuts like nobody's business.
I always do a couple of practice cuts & fits with a piece of drop-off & scrap t-molding just to make sure that I've set the depth properly.
I use T-molding.com's stuff & it fits tightly into the slot.
I have to use a rubber mallet in order to drive it in all of the way.
I get a lot of use from both the guide & the cutter.
If you forget to drill your plexi at the same time as your panel (come on I know that I'm not the only one who has done this), you can fit the plexi to the panel & use your Dremel with the guide & a small drill bit to match-cut the button & stick holes.
The tungsten carbide cutter also works great on metal, plexi or anything else for that matter (including flesh so be carefull).
Hope this helps.
Z