How can I cancel and replace a Transaction that never gets confirmed? According this this WikiPage, a MultiSigTransaction that doesn't include a fee may never get included in a block.

Since I've read that replacing Transactions (by version number or any other feature) isn't enabled, how can I expedite the replacement and updating of this?
You could import the private keys used into another wallet and spend the funds there.  For instance, on Blockchain.info/wallet you simply do Advanced -> Import and import the private keys (which can be exported from Bitcoin-Qt's debug console).