Hi John,
Officially, there is usually no way to uninstall an add-on once it's installed (short of resorting to a backup taken before it's installed). For a sandbox system, that's not usually a problem, as you just restore from backup or refresh from another system to recreate the environment, but I can see that this could be a problem for a development system if it's been a while and you can't afford to go back to an old backup. Some add-ons have 'uninstall' packages available from SAP that you 'install' via SAINT and that process removes the original add-on. Others can be 'passively' deleted during an upgrade.
If none of these apply to you, and you don't mind some risk and a completely unofficial process, you can have a look at thread http://scn.sap.com/thread/3198478 where I discuss how I ultimately solved my problem mentioned above. Use at your own risk. Not at all officially sanctioned. But it worked for me.
--Matt