In reply to peebles boy:
From memory seeing the prominent East Ridge of CDM (II) is a good indicator that you should start looking left to pick out the summit ribs, there are sometimes some icy runnels before the main ribs. The East Ridge is big enough, and steep/black enough you can often see it when the summit ribs are in clag. GPS and a grid ref does sound useful though.
Western Rib is also a good route if you end up on that by mistake, and I'd recommend the couple of pitches of III ice up Spare Rib Gully, where you can then get up onto Western Rib. You can often spot the ice of Spare Rib Gully through the clag, but not sure if it will have any ice at present! Daim Buttress is ok too.
They are all long routes, and well worth the walk in and out, even if you did miss the last gondola.