I had leftover threaded rod and sub-par frame vertices, so I threw together a spindle based on this: http://www.thingiverse.com/thing:4337.
Makerbot sells a box for $95, but it sounded expensive for a box. I think my solution will total less than $8 (at the most) and sit neatly on top of my MakerBot. Keeping things simple and compact as possible were my priorities. I love that Mendel parts will be feeding the MakerBot! I will post a pic when it is finished and mounted. Filament issues have caused many failed prints. I have not seen anyone use this simple approach on the CupCake yet…. send me pics if you have!