This is a modification of the mendel foot to combine it with a scaled version of http://www.thingiverse.com/thing:3088. It also mates with the Mendel y-bar-clamp to avoid the need for an extra part. It also looks cute!

Print two left feet (feetwithfeetL), two right feet (feetwithfeetR), and four y-bar-clamps ( https://reprap.svn.sourceforge.net/svnroot/reprap/trunk/mendel/mechanics/solid-models/cartesian-robot-m4/printed-parts/y-bar-clamp_10off.stl ). Attach to Mendel. Enjoy! The holes go right through so you can use standard M4x40 bolts and M4 nuts. Stick nuts into the holes (may need some cleaning to go all the way in) and attach them to the lower two bars of your Mendel with the y-bar-clamps. I had to import the foot model into AOI and reexport it to get OpenSCAD to recognize it. I'm including it (scaled down) as part of the "source".

UPDATE: Mine printed with the holes a bit too small, so the m4 bolts could grip without nuts. So I guess nuts are optional. If the nuts don't fit in at first, you probably don't need them.