Waddlers.
There are guys around who are willing to do type test but at the end of the day, this is going to be an expensive exercise. The CAA used to allow a one off dispensation to use a non JAA sim and a non JAA TRE which would enable you to get the job done at the same time as your current base check. However, this option was withdrawn two years ago so you are looking at something in the region of a £1,500 expense (£3,000 for 2 candidates).
I'm not sure if it's worth it in my case as I am returning to fly the 757 and was just hedging my bets for the future.
PM me if you need any more information. I have heard from some UK TRE's and a company called Exact Aviation also provide the necessary. Check their website.