Do you really need MPA involved in it? If you just set up standard php includes so that we link to the site with ?123456 at the end of it & then you link to the sites with the include set to insert 123456 into the link, I think you'd be all set.
I think Bling Cash used MPA & has HFS (that are kinda stinky) - might give you an idea on how to set it up
