So basically, the answer is 'don't know' or 'can't be done'. I think this is a huge and growing problem that is going to be quite common given the way google is now bombing sites for over optimisation of backlinks etc. If you need to move forward in real business world timescales you often have to use a new domain and start fresh. You cannot 301 the old domain because in most cases it WILL pass any penalty on to the new site. However, you might have branding and some traffic arriving at the old site which you dont want to lose.
You then get to the point of my original post which if I can clarify it again is:
How can you get traffic arriving at old domain to arrive at new domain without passing a google algo penalty (which a 301 will do)?