It is possible to do this: when I looked at the bus/train timetable and saw the bus only took five minutes I figured it had to be. It took me about 25 minutes dragging a (lightish) suitcase. Walk straight out of Montchanin, turn first left tehre’s a sign), then left again at the roundabout, which puts you on to the new road down to the TGV station. It is mostly all lit, but given that there’s no pavement (footpath) it could be a touch hairy if you were doing this in the dark.
(It might prove necessary because the buses are very irregular.)
Just thought this info might come in handy for someone who’d otherwise have to do what I did – cross your fingers and take a punt…