All you need to do is get a few old rear wheels, take the cassettes and spacers of the hub buy using a tool called a chain whip and a cassettes removal tool. Collect enough spacers and a 15 tooth sprocket. Then fit them to you trials bike hub, make sure your crank sprocket is straight with the rear sprocket when you put the spacers and sprocket on your hub, use your derailleur as a chain tensioner, it'll cost you nothing. hope this helps