I thought about using a piece of 1/2" PVC pipe to slide over the seat-tilt-release handle as an extension. I originally thought about using regular white PVC pipe, but my local Lowe's only had it in 10ft lengths that wouldn't conveniently fit in my SUV. I then saw some Grey Schedule 40 1/2" PVC conduit in the electrical section and they had it in both 5 and 10 ft lengths. I only needed 1 foot or so for this project, so I bought a 5 ft length. The following picture shows what I did -
The grey PVC should be easier to see than the short dark-colored stock handle. The 6" length I tried on the passenger seat tilt handle was a little too long and could possibly rub against the seat bolster, so I used a 4.5" piece on the driver's side. The Schedule 40 1/2" PVC Conduit was a friction fit to the handle, so I just used a hammer to drive it onto the tilt handle, being sure to position the labeling down so it wouldn't be visible. If the pipe starts to come loose, I'll just use some glue to redo the connection. This is a great project for a group project since a 5ft length of pipe would make 13 4.5" pieces or 6-1/2 pairs. The 10ft length would supply 26 pieces for 13 Slingshots. The price difference between the 5ft and 10 ft lengths was less than 50 cents, IIRC.
I thought about offering to mail a set of the cut pieces for a small postage fee, but the postage cost would probably be more than just buying a 5 or 10ft length at your local hardware store. It would make more sense for a group effort during a garage day.
