I do not know crossdresser but as I remember WW has option to convers prop.

Anyway I think it is easier to convert dynamic clothes with cloth room.

In first frame pose V4 to hide her under clothes. In 10th frame set her in default zero pose. When simulation is finished export prop as an obj from 10th frame. Late you can import and save as prop.

More details you can find here:

http://www.renderosity.com/mod/tutorial/index.php?tutorial_id=2154