FCP is so unexpectedly cool. They really did ask the right questions and solved some important issues.
A split is a split, Left Right, what are you talking about, or should I say what is your client talking about, if you have a person talking and all his/her track is on ONE track there is not left or right its mono full on. One track can not contain a left or right.
Click on the timeline, go to the sequence menu, select settings, click on the dual mono radio button, select from the drop down menu how many track you want, click OK.
Go the timeline, on the a1/a2 icons click control and mouse click (or right mouse click) and select which track you want that timeline track to go to, IT WILL BE MONO, IT WILL GO OUT ON ONLY THAT TRACK! If left means track 1, and right means track 2, you know the rest.
Bada BING! Apple saved the day with that one.
Chris