Add Custom Date to iCal is an AppleScript that allows a person to add an iCal event from within the Address Book application. It is named simply "Add Custom Date to iCal".
Installation is as simple as copying a script file into a designated folder. And using it is done through Address Book itself, since it merely adds a contextual item to any Custom Date fields.
Support for nicknames and event recurrence is built-in. The iCal event also has an alarm attached by default.