Yes, small custom made ones work very nice. I have a 2", 3", 4" 5" 6" and an 8" that I made (plus a 12" and my bowl rest)
If you take stock the size of your banjo, you can hold it in your scroll chuck and drill a hole to tap it to 1/4"-20 Now pick up some angle iron and cut one to length. Drill a hole in the angle iron and using a hardened grade 8 bolt and a "star" lock washer, bolt it on nice and tight.
If you drill a clearance hole in a block of wood, sand a relief on the corner that fits into the inside of the angle iron and add two small holes on the bottom of the andle iron you can screw the wood down. (you could glue the wood to the tool rest too if you like)
On mine, I welded them in the same manner as the bolt method I mentioned, but this can be done with very little in tooling. If you have a steel supplier in your area you can ask them to cut metal stock to the length you need it and it will noct cost you all too much. You should be able to get five posts for under $10 or $20 all cut to length. You could cut it youself, and make a jig on your lathe to hold the stock 90 degrees to a wood face plate with sandpaper to square it up if you do not have a disk sander.
This should give you an idea how to make them for the cost of some metal and a 1/4-20 tap.
These were my first ones, I later decided that they were better with the wood flat from edge to edge like a triangle.
BTW, these tool rests use the metal edge of the angle iron and while you do not "need" the wood, they sure seem nicer with the infill than left blank.