Now that is interesting becuase the longest bolts I have found are 50mm but they have thread running the whole length of the shaft:

LONG wheel bolts 14x1.5 radius 50mm vw audi mercedes on eBay (end time 26-Aug-10 19:26:48 BST)

I think I'm going to have a breakdown!

I may well have to order the bolts from the US after all. Or I could possibly just not use the spacers and mount the 35ET's directly to the rear hub?