Hi Steve,
The url manager in mojoportal is not designed to do the kind of re-writing you are looking for, there may be some IIS module that can do that kind of url rewriting.
In mojoPortal the friendly url is always relative to the root like http://somesite/[friendly-url.aspx] , so the friendly url for that is stored in the db as ~/friendly-url.aspx and it maps to the real url which is a real page ususally passing some params in the real url. Pages in the menu of mojoPortal are all handled by the real page /Default.aspx?pageid=x
So an url like http://www.myoffice.company.com is just a root url there is no friendly url to detect since there is nothing after the root.
And the mojoportal url manager is not designed to map or redirect from one virtual url to another, only from a virtual url to a real physical page.
Hope it helps,
Joe