I know normally they ship BTO's direct from China (i.e. start the production line on your specific machine when you order), but I genuinely think they have produced a batch of each version of the config way in advance and have shipped all those to a central location in Europe.
How many combinations of BTO could there be? two models of 15-inch + two 13-inch with 4 configurable options each, so maybe 20-30 permutations? (someone better at maths can calculate the actual number

). They pre-make a few thousand of each permutation and ship those direct to Europe - enough to cover the first 2-3weeker batch. Any left over form the first wave of the second batch. They then follow on with true direct from China BTO's following that.
My money's on all our batch 1 laptops being in a European warehouse as we speak. Just thinking out loud