I would hazard that a discount is very doable. As stated above, stock is high and from what I hear, new orders are not where MMC or the retailers want or need them to be.
My suggestion is to try and get some options thrown in at no cost and be clever about it. For example, it costs very little on the production side to go from the standard black and cloth interior to the full leather. There is cost already baked into the car for said interior. And considering the tan that was standard last year is now circa £1500, most of that is pure profit. Same for paint. It doesn't cost MMC nothing more to paint a car in one of the standard colours vs. one of the non-bespoke offerings. Same goes for contrast stitching, quilting etc. Most of those design details would be a good starting point from a discount perspective.
Good luck
P