manuals can be left in gear and when you hit the remote start, they dont really care that they are still in gear, they can take off. a friend of a friend had a porsche with remote start and his kids were playing with the keys and the car took the washer and dryer through the back wall of the garage.
however, compustar offers i believe the only manual compatable remote start systems. you have to leave it in neutral when you exit the car and it will let you start if it was left in neutral and nobody has entered the vehicle since you got out and locked the door. if someone has, it figures the risk is too great that it could have been put in gear and it disables the feature.