AO with logarithmic depth buffer?

Question for the well versed in shader arts.
With depth buffers like this:


Is it going to be possible to create at least semi-decent AO shaders? For me it looks like a fat chance.

The issue here isn't so much that it is logarithmic, but rather there is no actual depth info on the characters. In other words, your AO will be on the background not the characters.