On your computer, make another "account" (maybe Mrs. L). On that second account, maybe you can install the UK Kindle app.
If that doesn't work, uninstall your kindle app. When installing see if it asks if you want to only install it on your account (or your whole computer). Choose for just your account. Then go to the new Mrs. L Account and install the UK kindle app.
Personally I'd try this first before I'd go Virtual PC or a dual-boot system. Those just seem like a pain whereas if my method works, it would be relatively painless.
De-DRMing books is just a temporary solution. I feel it will be a pain to do that for every single book. Also, you don't get those cool whispersync features :P