2 pc's, 2 live 4's.. and i don't wanna stop

[PFX808]

to me, one of the major letdowns of live 4 was not being able to open 2 live sets at once, which brings me to my issue; i want to be able to run one live set ('track'), and then slowly bring in the next live set ('track') in sync, then continue this process back and forth.
setting up a master/slave has it's problems, i can run the master set, then bring in a slave set, but then i wouldn't be able to open another set in the master because i'd have to stop and close (which would stop the slave). am i missing something about midi?? is there a solution for this. at the end of the day i want to be able to bounce between 2 pc's loading up a new set each time. i'm not prepared to pu all the data into one MASSIVE live set though..

thanks heaps

alex