Balance Pool Strategy
By default Antminer S1 use Priority as pool mining strategy. It will use Pool #1 as priority to mine and #2 and #3 as backup. If you want to change the pool strategy to Balance, just modify file /etc/config/cgminer and add following line:
option pool_balance '--balance'
Antminer S1 will do evenly balance the mining to available pools.
Hope it help. Happy mining!
Note:
I had tested it with latest firmware.
It's been part of cgminer and in the cgminer README for years

However, you would want to use --load-balance, rather than balance.
The default mining strategy is 'Failover' as per the README:
FAILOVER:
The default strategy is failover. This means that if you input a number of
pools, it will try to use them as a priority list, moving away from the 1st
to the 2nd, 2nd to 3rd and so on. If any of the earlier pools recover, it will
move back to the higher priority ones.For any version of the ant:
Adding --load-balance with a space after the first password on the luci "Miner Configuration" web page will work also.
e.g. if your "Pool1 password" was "pass" then set it to "pass --load-balance"
Not sure if you can do pool_balance '--load-balance'. I am checking into /etc/init.d/cgminer, it construct the command line using -o (for Pool URL). Thus in load balance mode, we need to use -U / --quote.
From CGMiner README:
--quota|-U <arg> quota;URL combination for server with load-balance strategy quotasLOAD BALANCE:
This strategy sends work to all the pools on a quota basis. By default, all
pools are allocated equal quotas unless specified with --quota. This
apportioning of work is based on work handed out, not shares returned so is
independent of difficulty targets or rejected shares. While a pool is disabled
or dead, its quota is dropped until it is re-enabled. Quotas are forward
looking, so if the quota is changed on the fly, it only affects future work.
If all pools are set to zero quota or all pools with quota are dead, it will
fall back to a failover mode. See quota below for more information.I did modify the /etc/init.d/cgminer to accommodate load balance with quota strategy. If anyone interest, PM me.