Using (aa), (bb), etc. as automatic row number?

[Brian Vito]

Is it possible to set up automatic row numbering to number rows in the form 
(aa), (bb), (cc), etc.?  Getting it to do (a), (b), (c), isn't a problem, 
but I can't figure out how to double the letter.  Note, this is the 
numbering format used by some federal statutes, so it would be helpful to be 
able to reproduce using OmniOutliner.

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