In reply to John Aisthorpe:
Doorstep skis have some sneaky ski stores dotted around Morzine which i'm sure you could get a few bikes in. From what i remember there's a big ski store underneath L'Aubergade Hotel which you can get access to for about €10 for a week (For skis, so potentially for bikes)
If that's no good i'd just get them to go and speak to a few of the local hotels, they will surely have some basement ski stores with spaces provided you grease some palms.