Exact same machine, exact same problem!
I use mine for DJing - and as you can imagine this isn't the time of year for this to happen - pick up a new pro on Tuesday.
However if there's a fix, it'd be nice to have a back up machine ( I never thought I'd need one to be honest)
I've looked on the net and most people are saying GPU issues.
Gonna strip it down and take the logic board out. Might look at reflowing it ( got nothing to lose) or see if I can track down a logic board (although buying a new MBP was probably a cheaper option!)