Perhaps people's birth certificates should be stamped with team they are allowed to support.
Send the details on a couple of CDs to all clubs, so they can turn away any plastic fans.
Turning away from south London issues for a moment this would certainly spell the end of all those 'great European nights' at anfield. And what a relief that would be to the rest of the country. Not to mention all the wifes and kids in Cornwall and Norway who'll have their menfolk at home for a change.