That's correct, the diamond cut 403 19" wheels cannot be insured through ALA.
I've insured my 18" painted ones and got a discount on wheel insurance as I have GAP with ALA.
ALA use Revive for smart repairs to alloy wheels.
http://www.revive-uk.com/
Now I just wait for Saturday 22nd Dec when I'll be one of the BMW Boyz.
Oh, I've decided to keep my GTI for winter driving/commuting. The Beemer will be in partial storage.