Actually, I think you can. There's probably some linux utility you can run at the shell prompt. Don't have a link to one handy at this time, but I'm sure someone else will jump in here and help out.

One thing is that you'll want to clear the metadata on the fixed tracks and do a re-synch. This way it can properly re-calculate the offset from the beginning of the new header. I think that'll work, not sure.