iControl Method to Disable Pool Member

Assuming this is for the LTM module function, it looks like you want LocalLB::Pool::set_member_session_enabled_state:

https://devcentral.f5.com/wiki/iControl.LocalLB__Pool__set_member_session_enabled_state.ashx

The description reads: "Sets the session states for a set of pool members. If session state is enabled or true, this means that new sessions will be allowed to be established with the pool members."

Though I've not tested it, it appears that setting this to false for a pool member should be the equivalent of disabling the pool member (that is, it continues to process persistent and active connections, but no additional connections are directed to it):

http://support.f5.com/kb/en-us/solutions/public/13000/300/sol13310.html?sr=33964386