I recently bought a pretty spiffy (does anyone say "spiffy" any more?) all aluminum cupholder for my 911SC, which would probably work on the 968 as well...
It attaches with a single clamp screw to the front of the passenger seat inside seat rail... sort of slips over it, and then you tighten the clamp... it is in the shape of a paddle, with the large part cut out to hold a variety of drink cup sizes...
Very nicely finished in black anodized aluminum, very solid, and fit the Porsche design very well... I will have to snap a photo and post it for all to see. Now if I could just recall who is selling them... none of the usual "Suspects", unfortunately...
Try Googling Porsche Cupholder and see what you get... the only donwnside was that it wasn't cheap... maybe $40.00, but for a very nicely machined part, it looks to be worth it! And, if you don't want it in place, it fits in the glove box....