Have you ever considered adding an editable synonym substitution list? Looking in my list of tags I have several tags that mean basically the same thing (ie. MN=Minnesota, AHA=American Heart Association, nursing=nurses, etc).
I understand you have the ability to block 'noise' so I guess you could keep one of the terms from being created but you run the risk of no term being created at all then for that post. Has anyone else seen a need for this?