Pick up a British magazine, like PB or Bike. There's always a million ads in the back for insurance, and I'd be willing to bet that one of them would pick you up for a short term contract.
As an aside, I plan to ship my bike to southern Italy in 2008, tour part of Europe, and then ship it home. What company did you use to get you bike to IOM? How much did you pay? What kind of timeframe did they give you? I'm interested to see how you arranged it, and how it works out in the end.
Hi - This is what kept me from taking my bike to IOM 2005, so we rented instead. None of the UK firms would cover us without a permanent UK address. I guess we could have faked that, but that probably would have been an excuse to not pay if something DID happen.
Anyway, we're planning for our 2008 TT trip, and I found a guy in Phoenix who can insure you. Go to www.berglundins.com or call them at 1-866-702-9253.
And I'd be very interested in hearing about your shipping details.