Well, if you want to do it yourself, you could:

1. set the preteen's spandex morphs
2. export the figure mesh in its morphed state
3. reimport it and use the grouping tool to highlight those parts you want to keep
4. spawn a new prop
5. bring it into the setup room to make it a posable, conforming figure

Or you could save yourself some time and hair, and buy the3dwizard's Preteen Bodysuit over at PoserPros.