Numbers 2: Create a new header cell, listing once the contents of a column
Here is the solution that worked for me. 
The original solution was provided in a question I posted in Apple Support Communities.

I am posting it here, as an answer to anyone the might arrive here looking for the same solution.

The 2 Cell Functions:

=IF(COUNTIF(A$1:A2, A)=1, MAX(B$1:B1)+1, "") 

=LOOKUP(COLUMN(),  First::$B, First::$A)




Original Answer: https://discussions.apple.com/thread/5960924