why not take the outer boundary of a viewshed, convert it to a polyline and use it to extract the elevation profile?
Thanks for this suggestion. I tried something like this at some point but had so much trouble with erasing all the 'non-visible's from the 'visible's in the viewshed raster, I gave up. Also, the final graph needs to relate degrees with elevation points in meters.
I'm going to put up another thread explaining what I'm trying to work out. Thank you all for your help.