Not exactly a slider but this may work for you. When I installed an in tank electronic fuel pump my new fuel lines needed 1/2" additional height to miss the bottom of the seat. All I did was fab aluminum 1/2" spacers for the seat mounting points. What you might be able to do is use steel instead of aluminum and make the spacers longer to allow the seat to sit further to the rear. Drill the front hole to allow the spacer to bolt to the factory location. Drill and tap the rear hole for the new seat mounting location. Bolt the seat into the new location and you're done. The seat won't slide but it will allow for additional leg room.