Copy the .craft file from the SPH to the VAB. Then you can launch it from there. It will say the craft's not supposed to go on the launchpad, but it doesn't matter. make sure you are in the KSP/saves/WhateverYourSaveNameIs/Ships/ folder, not the KSP/Ships folder, or you will be seeing the stock crafts. Unfortunately, this will put you on the launchpad, not the runway. You might want to put some transportation mechanism around your aircraft to move it to the runway.