Your suggested mounting location is great but I would like to recommend this collapsable cupholder by FISCHER (made in Germany just like the Crossfire). It is less expensive, requires no modification and it folds up when not in use
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Fischer Cup Holder $14.99 - Ultimate Cupholders - Cup holders for 5 Series and 7 Series BMW, Z4, Porsche Boxster / Porsche 911 996, Mercedes, Audi, Acura NSX and other fine cars. The ultimate cup holder / cupholder!

It is currently also on E-Bay and that seller has some nice photographs worth checking out.

Made In Germany FISCHER Drink Cup Holder Ferrari Porsche VW BMW MERCEDES BENZ | eBay