Had the same problem with '06 FL1 17" alloys.
No space round the back for chains and French want them or you no-go up the mountain!!
Went for a set of Maggi Track -
http://www.maggigroup.com
Available thro' roofbox co. & others in uk.
They fit securely using a hand wheel clamp onto the outside of one of the original wheel nuts (check your nut sizes) - no hubs, plates or other fittings or extentions to attach before you start out. They fold flat (really flat) into a small 20" long holdall that sits behind the rear seat out of the way and really do only take a couple of minutes to fit. Fit the clamp onto a wheel nut, open spider with chain already fitted, drop chain onto top of wheel and move down each side as far as possible, pull the tensioner in centre - do other side the same and then drive forward and they really do self centre.
Didn't believe it would work until I did it myself.
Have only used them for test runs as yet - no snow up the pass when we went - but we were ready and confident that we could get them on in the dark when it was cold & snowing!
And unless the French have changed their tune snow socks were
not allowed but michellin have recently started doing a bungee based chain with metal staples that may have affected their stance? Best check before buying either. (both types go behind the tyre and move out as the wheel rotates - clearance issues?)
Couple of others I looked at were Spikes Spiders and Michellin Easygrip.