Use a computer. So much easier.
But if you don't have a choice, I think you can do this in the Song Creator by marking the section you want to "double" (for all tracks)(by setting start and end points, I think), then "copy" it, set the location at which you want to paste the data back, and "paste" to this location.
I haven't ever done this, mind; I would worry about whether the information you are pasting will be inserted (all following song data is preserved but moved to follow the inserted data) or will overwrite the existing song data. Clearly you dont want the latter!
Hope this helps.