Deb added some handy examples to the codeshare section here:
http://devcentral.f5.com/wiki/default.aspx/AdvDesignConfig.CodeShare
Click here
Check out the cURL examples for something to get you started. Reply with your testing and any issues if you run into problems.
[Edit: SOL7444 has some helpful info as well]
Note: Beginning in BIG-IP LTM version 9.0, you can use an external monitor to monitor the status or health of a node using an application that is separate from the BIG-IP bigd health-checking daemon. The same behavior is achieved in BIG-IP version 4.x using an EAV pinger. For information about the requirements for an EAV output, refer to SOL1561: Requirements for EAV output.
By default, the bigd health-checking daemon assumes that any stdout messages sent from the external monitor to the console equate to a positive response, where the node is marked up.
When a node is up, the external monitor will print data to the stdout and bigd will mark the node up. When a node is down, the external monitor does not print data to the stdout and bigd will mark the node down.
Important: If a node fails to meet the external monitor criteria, the external monitor should not send any data to stdout. If you create an external monitor that displays a node as up, but also displays down, the bigd will interpret both responses as up.
Aaron