Very hard... You would be cursing trying to do it.
If you can get to the back, you still need to get an old welsh plug out, and then somehow tap the drain in.. I would most likely say NO.. but it could be possible with a few broken nuckles i would say..
Sorry best done with engine out, as you still need to plumb this back to the sump or i have heard of people plumbing back to remote oil filter (not sure if this is a good idea though).
Karl