Alphanumerics with UCC128 barcode


I have the following zpl code
^FO25,215^A0,N,25,25^BCN,100,N,N,N,U^FN21^FS The customer wants this barcode as a UCC 128 barcode, but their data is alphanumeric. I looked through the zpl docs and it mentions that if you pick option U for the mode it defaults to Subset C, which automatically strips out the alpha characters.
It further mentions that I can prepend the entry with >9 or >7 to make this Subset A which allows alphanumerics. But when I try:
^FO25,215^A0,N,25,25^BCN,100,N,N,N,U^FN>721^FS It still removes the letters from the barcode. Not only that, but it adds 7 as well. How can I get alphanumerics in my barcode?