I don't think you will get any discount out of the Grand Seiko boutiques without a history of purchases. I think @Soul got discount from a distributor (can't remember which) on his snowflake. Watches of Mayfair seem to offer discount on GS, but don't know if they would source the model.
Watches of Mayfair are grey market not AD, hence the solid discounts. I shouldn’t think you’d get much of a discount out of the London GS boutique, if anything. Which sucks because it seems that ADs in the US are pretty happy to.
I don't think you will get any discount out of the Grand Seiko boutiques without a history of purchases. I think @Soul got discount from a distributor (can't remember which) on his snowflake. Watches of Mayfair seem to offer discount on GS, but don't know if they would source the model.