Well, I thought things looked clear a couple of hours ago, but hearing these stories make me think again. Running a brand new tyre with a part-worn tyre on the same axle on a car that is even halfway fast is plain irresponsible. For all the silly laws we get from the EU, we don't get sensible ones that prevent lease companies doing things like that.
At 1.6mm of tread, are you at risk of getting nicked? Can't say I'd want to go anywhere on a main road in the wet at that.
I think I'll just go my original plan and leave the service package (or whatever it's called) off, get rid of the RFTs and put on some proper rubber - probably Michelin Pilot Super Sports. Better ride, better feel, better grip, more planted-ness & safety on twisty, broken road surfaces. Also very expensive, but I hear they last incredibly well compared to the PS1s & PS2s.