Whirly,
It would be nice if we could have a frequency for blind calls. But there are pilots out there (and I have in mind some well trained (ex mil) pilots) who simply hate using the radio and would not use it. What is more, the standard of some pilot's navigation and RT would mean that it would be useless anyway.
Perhaps we should all remember the rules of following line features, after all we are talking about the M25 corridor.