There's no reason that you can't, other than how close the working distance will end up depending on the length of the tube. There are no extensions tubes yet made for m4/3s, but I have asked RJ Camera to look into this and they say we'll likely have some available this May. They are also working on tubes that will allow one to use microscope lenses on m4/3s and other cameras.
At times, one of those can work better, as there's no light falloff and you can still get increased magnification. Make sure that whatever you buy is a 'doublet', that is, it consists of two lenses sandwiched together, as these provide much better quality than a single lens.
Adapters for using microscope lenses are already out there in case anyone's looking. I just picked up an RMS to M42 adapter for about $30, and I'm using it with my M42 adapter/tubes on my GH1. Just waiting for some microscope objectives.
OTOH, I can't wait to see the RJ tubes for m4/3. Hopefully they have the electronic thru connections.