Sounds pretty dubious even if it can be done at all. Woot was selling refurn 4gb fuzes for ~30 bucks shipped a couple nights ago--is a bunch of SMT rework worth your while for such a cheap device?
On the other hand I've been wondering if it's possible to transplant 8gb of memory from a Clip to an M200 v4 which uses similar hardware. I like the m200 form factor and battery better than the Clip, but the m200 series now only goes up to 2gb. So the transplant would create something that Sandisk and everybody else doesn't seem to offer for sale.