Okay, I think I found something.
I just remembered that a while back I bought an external 3.5 IDE drive enclosure.
Back then I thought it would work via USB, which it did not (they sent me a wrong one).
Well, today I was looking at it and decided to do some research. It turns out that they company that makes these enclosures also make a PCMCIA version.
http://www.vipower.com/products.htm
So, I sent them an email asking which one exactly should I purchase. Those things are rather cheap - $40 at most (with all the shipping costs). This would be a perfect solution. It would also let me connect other things to it, like desktop CD-RWs and flash card readers. I don't need any of that, but that still is a nice thing to have. And I will be able to connect that to my next carputer system which I'm more than 100% sure I will build when I get a new car (long term planning
)
If I get that thing to work, I'll post here what to buy, how to power it, etc, etc.
I think this will help a lot of people in the future.