here's an option. create a system environment variable (ie: DefaultPrinter), and set it's value to the name of the printer you'd like to set as default. then use this script to read that value & set your default printer:

$ValueName = READVALUE("HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment","DefaultPrinter")
IF @ERROR = 0
SETDEFAULTPRINTER ("\\LocalComputer\"+$ValueName)
ENDIF

hope that helps.
-BDA