Has anyone modified combination stop/turn/tail lights to independent turn signals?

I changed my rear bulbs yesterday thanks to a slowly-dying right indicator, and I noticed something interesting: although in function the upper parts of 04+ tail lenses is just tail, it uses the same 3057 bulbs as the combination lights. Because I plan on making it to Scotland eventually with my car, and because MOT regulations include a need for independent rear indicators, I wanted to find out if anyone else has made a similar retrofit. I just talked to Infinitybox to find out if they had products that would work; the tech I talked to said their systems were overkill for what I wanted, and that a trailer harness would do the trick! Any thoughts?

I did a little poking around, and to my pleasant surprise Google sent me to a site that sells 2-to-3 wire adapter kits; meant for flat-towing a car with separate indicators by an RV or pickup with combination tails, the module takes the stop/turn feeds from both sides and splits them from the brake signal. For making sure all 3 brake positions light up when the hazard flashers are on, I figure a second lead directly from the centre light to the output end should work.