iRule to Enable/Disable pool member

How about use an iControl script for this? You could have them run a powershell or bash command that would be a part of their deployment or maintenance runbook.

Also, you could have a health monitor that they update a file, again either in a script or part of their task list, and the pool member would disable based on the monitor going down.

There's plenty of examples for either option on devcentral, if you need help after trying them out, let us know!