I have actually submitted this idea through their website, but I thought I'd post it here, both to get your thoughts, and to create a record in case they try to steal my story

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Starvin' Marvin Returns
The story opens on the planet Marklar, where Starvin' Marvin has been loaned an inter-stellar spacecraft to allow him to return to Earth for a visit. Upon his arrival, though, he is immediately forceably adopted by Madonna.
A press conference is held by Madonna to announce the "adoption." Stan, Kyle, Kenny and Cartman see it on TV. This gives Cartman an idea: if he can get adopted by a celebrity, he could finally obtain the riches he so desires.
Cartman diguises himself as an African orphan, and goes to a TV studio where Donald Trump is filming his show. Cartman's plan is to become Trump's adopted son, as Trump clearly has the wealth Cartman is seeking. Trump is about to fall for the scheme, when Rosie O'Donnell intercedes and insists that she and her "life-partner" should be the ones to adopt Cartman.
A major battle between Trump and O'Donnell ensues, and Kenny is killed in the crossfire.
Ultimately, Cartman's true identity is revealed, the Marklar arrive to rescue Marvin, and in a typical "I learned something today" speech, Kyle and Stan explain why celebrity adoptions can, and often do, suck.