Is there a way to set a 4th pool in the web interface?
You might use the more option field for this, just append 4th pool setting to your avalon options, such as
--real-quiet --avalon-auto -o stratum+tcp://stratum.btcguild.com:3333 -O ur_worker_name:123456
Didn't tried it, but it should work. Why do you need 4th pool?