You need a ski jump on the end and a bit of aerodynamic cleanup, then you could let the rocket part do its thing. Sounds like your engines had the 'chute "pop" at the end, so you could use that and bring it all back to earth safely.
Better yet would be to work up some type of fusing system so that at the ski-jump part, the rail car separates and just the rocket continues on.
But I'm thinking too much....