Designed a surface model that had 4 offset surfaces (could be any number) at 0.4mm apart and brought that into the UP! software. Printed it with the "SURFACE" option checked and the "Unsolid Mode" checked in the print options.
One thing to note is that the nozzle prints along the centerline of the surface printed. The printed part's dimensions are hence affected. The outside dimension is 21mm (surfaces are 20mm apart) and the wall is 2.2mm thick. This means that the nozzle deposits a 1mm bead (0.5mm on each side of the line/surface slice)
Don't know if this is any use to anyone, but it may come in handy for some simple parts what require a thick wall.
I have been wondering if we will get solid fill on Windows at least as Microsoft seem to be stipulating specific fill standards for their 3D printer drivers though I am sure they will soften on the position and not enforce the requirement rigidly.