This is a weeble I created in Alibre Design PE.(Mostly to prove I could do it, and to get to grips with the way it models on planes.)If you have the ability to pause your 3D printer, or can otherwise play about, you can easily add a small weight. You can pour low melt alloy in, or drop in a 5mm lead shot or whatever - there is a walled void 5mm dia.x~7mm deep in there. It will be sealed safely inside by the printer.If you are using an UP! (as I am) you need to print two of these, or at least something else on the other corner of the platform, so the head moves out the way so you can pour/place your mass.