MOSS2007. SPWorkflowTask.AlterTask's last argument.

Question

MOSS2010 documentation for SPWorkflowTask.AlterTask method claims, that

If true is passed as the argument to fSynchronous, this method waits up to 30 seconds to determine whether the attempted update was accepted by the workflow schedule as valid. The method then returns true if the update was accepted and not rolled back, or false if the update was not accepted.

So, there should a way to reject (aka roll back) AlterTask in OnTaskChanged activity (and notify the caller of AlterTask of that), shouldn't it? But how would I do that? Should I set a magic task field to a magic value? Or is there a special method to do that?