Might be worthwhile trying to tempt National Express or some other bus/coach operator to increase the number of routes that serve LTN. There used to be a service from High Wycombe, but that was diverted away. There is now no practical way to get from High Wycombe to Luton Airport other than going into London or possibly Oxford and back out again. At least, I couldn't find one and I'd love to be proved wrong.