there seems to be a couple of different methods for modding the vdimm
the best one involves cutting one of the traces on the back of the board and adding a resistor so that the vdimm is selectable
another method is to just wire up the 3.3V rail so that you get 3.3V vdimm (or thereabouts)
i found a thread on XS regarding modding the MSI K8N Neo platinum (should be very similar mods)
unfortunately the pictures no longer work, maybe you could PM Hell-Fire:
MSI K8N NEO Plat Vdimm & Vdd Mods
and here's a couple of pics of the 3.3 rail mod on rebelshavenforum.com
Topic: K8N Neo2 Vdimm Mod