I think £5 might be a bit ambitious for the leisure traveller who wants to cut the corner off security, and jump in on scanner #1.
It might appeal to the business travellers on EZY who also pay for speedy boarding. Knowing that you can check in on-line, and turn up 30 minutes prior to the flight is reasonably valuable at 07:00 when you're only off to EDI or GLA for the day.
It would appear that *G fliers get a Fast Track sticker when flying on a *A airline. Myself (*G) and Mrs. BT (*S) were stickered when flying on SK a couple of weeks ago.
Mind you (as noted above), when we fly LH we appear to be paying £20 more for the privilege of using the same facilities, so maybe it's only fair?