This is a remix of http://www.thingiverse.com/thing:801279. I just took the 19x19 base (16 holes) and cut it into quarters (using Netfabb Basic) so I could print on my printrbot SM. Added some holes/pegs (with 123D Design) so the pieces will fit together. Just print it four times, clean them up (may need to clean up the holes so the pegs will fit nice and snug). There's also some extra holes for a small screw in case they are too loose and need to be held together better. Note these screw holes are very small and were not made with any particular size/type in mind, so YMMV. My print (two pieces so far) doesn't look like screws will be needed. I'll add pics when I can.
Edit: finally added some pics of the final assembled base. It did take some effort cleaning out the holes and pegs for a nice snug fit. I just used an Xacto knife to clean it up, then some pliers to gently force the pegs all the way in. I'm quite pleased with how it turned out.