One of my plans was to build this:
The Airborne Launch Assist Space Access (ALASA)
Of course the rocket part will be built in SR2, but the plane... ehh.... Phanps' F-15C will take care of that.
However, as what I see now, water and oil simply doesn't mix. I hope the Devs make SR2 SP compatible.
Ok, this is hands down best idea for the game.