I am almost ready with a complete e-mail // FTP separation. Changed only a couple of lines! I will post this to the tipps and tricks section.
I would deny to hack around on this subject further (like configurable FTP dirs or fully virtual mail users) - too much effort for a falling star ... ;-)
I think ISPconfig 3 is the real thrill now. I think I'm going to love it, although usability is much more an issue for v3 than for v2 - surprisingly. But that's always the cost of flexibility, if you look closer.