It might work but the host is adding and deleting portals all the time. This means the logic is changing. Maybe take the logic out as a usercontrol which gets dynamically updated on demand by the server.

Although I have a similar solution where a token is placed in the skin and replaced with the footer using an http module. However I have concerns over performance. Parsing the contents of the skins in every request is a bad idea.

Maybe using a modified skin and placing it as a site skin instead of a host skin might work.