Possible to make a plugin that loads external iframe dialog?

Ok, from the subject line you might think I want to load my iframe dialogs from an external domain, but no, actually what I want to do is load my iframe dialogs from a root directory on the website, like so.
/RPGTools/blahblaheditor.aspx

This should be quite possible, but when I deleted the code that generated a relative link and put this instead
CKEDITOR.dialog.addIframe('GameManager_dialog', 'Game Manager', '/RPGTools/dialogs/GameManager.aspx?TopicID=' + TopicID, 550, 400, function() { /*oniframeload*/
})
It still put in the plugin path, which is particularly aggravating because the plugin path it wants is the Source folder, which makes sense fine for HTML pages, but is going to cause probablems for my server side pages.

If anyone can give me a pointer I'd appreciate it.