surface tension
Wouldn't the surface tension alone compensate? The hard part would be getting the nozzle close enough that the plastic layer makes immediate contact but not so close that the nozzle fouls the print. With 3d printing on earth, I think there is a certain amount of slump or deformity possible if the plastic cools irregularly. Several 3d printers have the option of a heated bed to counteract this. Without gravity (or rather without the force of the table acting in response to gravity...freefall) I would think the risk of slump is diminished.
I haven't yet had the opportunity to play with a 3d printer, though its on my Christmas list, right next to quadrocopter.