A big "launch" is simply building an event and buzz around a sale/promotion...

So there's certainly no reason you couldn't do one.

Maybe add a bonus "The Special Crazy September Promotion... Reserve Your Copy Now To Get the Crazy Bonus" (please don't use the junk I just wrote there though... point is, think up a hook/story and run a sale).

Or do a "version 2" or "revised for 2009" etc promotion and "re-launch it".