I think the SUMP analyzer firmware could be tweaked to record ADC values (limited to 8-bits?) instead of digital bit values.
The SUMP client code could be modified to display a waveform instead of logic signals, or a different scope client could be used, like the VB6 one here:
http://www.semifluid.com/?p=9 (http://www.semifluid.com/?p=9)
I think the CSV/SVN version of SUMP might have an analog/DSO display mode. I'm not sure. It would be easy enough to make the SUMP mode sample the ADC instead of the PORT pins, but live display like in the example would need a new mode (not that it would be difficult to integrate).
If there's a cross-platform program that will display the output, I'll try to write host software for it.