Yes, it's possible, but you cannot benefit form the automatic placement feature. For this extra feature to work, TransDEM has to know where your Trainz route project is located. TransDEM does this by setting the Trainz World Origin object to a value specific to the route and baseboard arrangement which is difficult to calculate manually. Without a TransDEM-compliant WO object, the Google Earth images created by TransDEM are just a bunch of ordinary Trainz objects. It's up to you, where to put them.