Do not do this, I have a business lease for my car (in fact 95% of our employees have business leases), as I have had for my last 4 cars. If you read the leasing agreement it will more than likely explicitly forbid modifying the car in anyway (mine does).
One of my engineers decided it was a good idea to get a DTUK box for his leased GTD and then told me about it, thinking "oh, he's a bit of a petrolhead so he'll think it's cool" my actual response was very far off that particular mark, because of what I stated above. I asked him to remove DTUK box immediately, which although i have no power to enforce (after all the tuning box is his property) he promises me he has done. His car goes back in November so we'll see then if VW can detect it's use, if they can it'll be a massive blow to us as we'll have to foot the damages bill, and the engineer in question may have put his career with in jeopardy, and faces at a minimum some form of disciplinary action.
Sorry for being a bit preachy, but if you get any kind of lease your pretty much saying I agree its not my car and I'll hand it back in the condition I got it in, do anything else and its a massive, massive financial risk.
We also have an opt out option in the company car scheme were you can take an allowance as wages and buy your own car, which is what I would of done if it was my intent to modify my car, and what the engineer in question will be doing from now on.
