What is this port, and 3.5 mm DIY?

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Hi forum.

Several questions I hope you can help me with.

I have a 2004 New Beetle Convertible GLS that I just bought used (with just 30K miles on it), and like many people around the web I find myself in need of a 3.5 mm jack. I've seen the Blitzsafe and PIE solutions, and I've read the How-to thread here. Is there no way to rig up something DIY? 50-100 dollars seems awfully steep just to add a jack to your stereo. I've also seen this:

VW 8 PIN 3.5MM AUX INPUT JACK ADAPTER CABLE MP3 iPOD | eBay

And I wondered if that was any good. I've contacted the seller, but they're not writing back, of course. I've heard that these don't really work because the cd changer interface they plug into requires some sort of logic signal that identifies the incoming signal as from the cd changer. Is that true? Has anyone here had luck with something like this?

Next question:
Beneath the stereo, above the cup holders is a white plastic cap. If I pull it out, there's a wire socket attached to it that seems ready to plug into something. What? Is that for some of the optional accessories? Seems very strange.

Thanks in advance!

[MyOtherRidesAVette]

Apparently there are aftermarkets out there that will plug into a portion of the remote cd changer harness plug and I have read mixed reviews. Haven't seen any OEMs for $50-$100, maybe double that.

The white plug you are talking about is probably a filler for the red LED under console light for the center console, without seeing pictures of exactly what you are talking about.

The Aux Jack when the head unit has the feature, prior to '06, is underneath the center console where the seat heater switches are located. About and inch back and about an inch to the left from the right front corner.

MORAV