Are you referring to the use of external content in your site?
If not, I think you may have something confused with the way mojoPortal includes CMS content in the site. CMS content is anything one puts in a module or is generated by a module. This content is placed directly into the markup of the pages. iFrames are not used to show any content in mojoPortal unless one uses the iFrame Module.
If you are referring to external content, you may want to take a look at jQuery Load. I am currently using this on my site to integrate my support system (WHMCS which is PHP) into my mojoPortal site. I use jQuery Load to pull in my mojoPortal generated menu and some select content.
I think a module that makes the use of jQuery Load easier would be cool.