Nowbody knows how to do this? (MSI setup)

[Mogyi]

I am pretty amazed how this issue is handeld even by Microsoft. In custom action dll's the recommended rollback calling is throwing a InstallException (generates a error box about 'unknown' unhandeld exception). But what about canceling a setup during a custom action initialized dialog...??? Please, if somebody knows how to rollback nicely from custom action dll's please let me know. One more thing, maybe it's a setting or something but base.Rollback(savedState) called directly isn't resulting in a rollback, nothing happens. I'm so desperate, I will do other stuff for a day or two but my last hope of solving it will be hooking on the setup and killing that damned error message box...