Using cm_dontconvertlink="cm_dontconvertlink" now seems to remove the hyperlink completely.
Has there been a new release of the software - that's two things that don't work now that worked 2 weeks ago.
You actually just need to have cm_dontconvertlink in there, no equals sign or second instance of it.
So it should look like
<a href="http://www.myserver.com" cm_dontconvertlink>this is a link</a>
See http://help.campaignmonitor.com/topic.aspx?t=83 for the full help topic