I experimented with running one of my machines with 4 instances of the mining application, using 4 different worker names instead of lumping them all in once instance, and the payout appeared slightly higher. Because of variability in payouts in day-to-day mining I couldn't say it was significantly better so I ditched it - It was just more work and maintenance than it was worth.
You know you can use pools in cgminer to do this. Just give cgminer a list of pools and usernames, where every pool is middlecoin.com:3333 (or your closest server) and each username is a different address in your BTC wallet.
Then use --load-balance and cgminer will submit shares equally to each of the usernames.
