I made a quick jig to run flutes along some cool little muddlers I had turned.
Step 1: Build the sliding base
One piece of wood, cut exactly the width of the gap (2.5") and 6 inches wide forms the guide. Another piece, slightly larger (3"), goes underneath the bed and keeps the jig from tipping over or sliding out.
The gap was 1.5" deep, so I made another piece 2.5" wide, and slid it in between the two. However, it needed some sanding down to keep the slide flush with the top of the lathe bed.
Two pieces of threaded rod slid through all three pieces are for tightening your jig down. (with a nut on the backside or glued to the 3 pieces)
This whole slab slides up underneath the lathe bed and fastens to your jig
Step 2: Adjustable base
If all your pieces are a similar size, you wont need nearly this much adjustment, or this large of a base. The rotating section is completely unnecessary, but it does add a little more flexibility for doing interesting pieces.
Mine is 6" wide, and 12" long. I cut it out with the CNC Shopbot at TechShop to make sure the grooves and the arc for rotating were cut perfect. You can probably do it fairly easily with a router though.
Bolt it all together with some wingnuts, and you can fasten the whole piece to your slide.