With hydra media, you can change the end of the link to &l=2&frame=keep&s= and that should allow you to keep the iframe.
The only other way I know of would be to set the security attribute on the iframe:
<IFRAME SECURITY="restricted" src="http://www.microsoft.com"></IFRAME>
However, this method only blocks iframes from breaking in IE. Your best bet is to talk to your affiliate company and tell them you want to setup a co reg path. If they support co reg, then they should be able to help you out.