Chopper,
As far as I know, there is no easy way to display “user bits” within FCP. As I understand it, “user bits” are NOT an auxilary TC, but a “user changeable” data bank that can hold words like “Cam 10” or “Team B” or 9/25/05″. This “word” is then available on every frame of video via the main timecode stream. The word does not change once you set it. So, I don’t know how you would use this feature in lieu of regular Timecode.
I think you may be confusing the two different types of code with “user bits”. There are two types of timecode: record run and “time of day”. With record run, you set the number where it starts (typically hour one) and it will add uninterrupted timecode until the end of the tape. “Time of day” is set literally to the clock on the wall, and then updates each new start point according to that time. This results in many “breaks” in the code. Many NLE’s choke on this kind of code, and so most people hate it. Others (as in your case), use it as a convenient way of syncing multiple cameras. This choice is made at the source (camera) and once set, can NOT easily be changed.
In your case, unless you have a slate or “Common marker” on all three tapes, you’re going to have to sync by “in point”. Good luck.
Mark