I have had to deal with that at Terminal 2 at LHR.

This was when I was going to the previous Paris Air Show, so it was summer 2005. I was flying LHR-CDG on AF (Terminal 2) and since my carry on was over 7KG they tagged it for checking. They told me I had a good chance (off-line nonrev, I work for American Eagle Airlines) but couldn't clear me until close to departure time. So they told me to wait near the ticket counter where I could hear them if they yelled my name.

At 25 minutes prior to departure they called my name. I gave them my bag very quickly and ran for security. I missed all the shopping! It took at most 10 minutes to get through security, so I got to the gate in time to join the crowd that was already boarding. When I took my seat on the A320, I noticed that it was only 50% full. They could have easily cleared me earlier than they did.

Here's the bad news. The carry on bag that I had to check (and VS allowed me to carry it on their JFK LHR A346 flight) was lost for 4 days. I couldn't understand why it was lost because AF only flew to CDG from LHR at the time.

Anyway, that's my experience.

I am planning to nonrev on BA out of Terminal 5 sometime soon to see how the SMS messaging works for clearing you on the standby list, and to see what it's like in the new terminal.