Provide a Session Timeout Message and Allow Users to Extend

We're working on dialing in session timeouts for agents spread across the country. (Note: We are NOT using VPN in our BIG IP Setup.) For agents ease of use, we would like to give them a five minute warning for their 30 min session time out, as well as giving them a button to push that lets them extend for another 30 minutes if possible. Even just the reminder would be handy though.

I've seen some irules that that will auto extend sessions based on cookies, but am unable to find any that describe what we're trying to achieve. Any suggestions?