Well, I most certainly wouldn't be doing the same thing but it's your money.
I'd be doing it myself in their f'ing car park.
Exactly this, surely you must know someone that has a trolley jack, axle stands and can remove the callipers? Take the callipers away, get them fixed and refit.
I could see the dealer not playing ball though, probably giving some excuse about insurance on their property.
Have a wander into your local paper and appraise them of the situation and see if they are interested in accompanying you to the dealership to discuss you working on the car?
Sounds like you’ve got nothing to loose here now, even to the extent that I’d be seeking legal advice about getting the car fixed and then not paying the bill! See if they could argue this in a small claims court. Depends whether £1500 is worth the hassle or the principle!