The docs do not show that AS=STRING allows a format parameter.
Also, if you look at the format masks for a date or timestamp field, they both upper and lower case M’s. The lowercase M‘s suppress the leading zero for months one through nine (I believe)
This is a tangent, but I keep this little cheat sheet to get date formatting the way I want it:
<<Current_Date, MMM d, yyyy>> - Jan 25, 2012
<<Current_Date, M/d/yyyy>> - 1/25/2012
<<Current_Date, MMMM d, yyyy>> - January 25, 2012
<<Current_Date, MMM d, yyyy>> - Jan 25, 2012
<<Current_Date, MMM d, yyyy>> - Jan 25, 2012
<<Current_Date, EEEE, MMM d, yyyy>> Wednesday, Jan 25, 2012
<<Current_Date, EEE, MMM d, yyyy>> - Wed, Jan 25, 2012