You can use mtty to do this, but can I ask why? It doesn't preserve any of your customizations and is not easily converted back into something flashable so I guess I just don't see the point.
The only thing it's really useful for is if someone got a hold of a 6700 running a ROM we don't yet have already (official apache aku 3, WM6, for example).
Anyway, here's the info if by chance you're still interested:
http://www.geekzone.co.nz/inane/1119