The problem with the switchclaim would be:
Scum X claims Pinky Pie, but is in reality Rarity, Scum Y claims Rarity, but is Pinky Pie in reality.
Scum X who claimed Pinky Pie, flips Rarity, there is still, there is still a scum inside the Rarity pool.
Now if we go for a combination of 4 scum, and all three methods:
Scum X claims Rarity and is in reality Rarity, Scum Y claims Rarity, but is Rainbow Dash in reality. Scum Z claims Rainbow Dash, but is in reality Twilight. Scum W claims Pinky Pie and is Pinky Pie.
^you can do the math that is is probably the neatest combination of scum fakeclaims/realclaims... and as you can see this actually only needs two scum to fakeclaim and be able to anticipate claims, and with less claims open to be made, such fakeclaims become even less risky.
There is still another possibility in my eyes that is way too unrealiable and speculative.