So I was bored after finally finishing up some work for Magic Smoke Industries and saw this interesting thread: Custom Control Pad
It had me wondering because I'm also a musician and I purchased some time ago an app for the iPad called TouchOSC to control synthesizers via MIDI. After searching I discovered that there's an application called GlovePIE that will convert Midi to keystrokes/mouse control and vice versa.
So using TouchOSC with TouchOSC Bridge (a utility that will connect the iPad to the PC via wifi) I was able to control KSP using TouchOSC. I present you a quick demo I cobbled together. Neat thing is you don't need TouchOSC, just any midi controller will work. Got an old midi keyboard and want to control using your keys have at it!
Some things to keep in mind. Using this setup will not allow you to get any feedback from the game (clock counters, text information) since it's essentially 1 way in this case. Sliders don't work in this case since I never tested the PPJoy virtual joystick with Windows 7.