I bought a set of those lower dash pieces from eBay a couple of years ago for not too much money. You can dye them easily if you don't find your preferred color.
I don't remember exactly what the shape of the back of those vents is, whether it's rectangular like the little vent, or transitions to a square, but you should be able to connect the VIA flexible duct to it without a lot of trouble. I used some stretchy-rubbery tape (not duct tape exactly, but something similar) on my second gen that I built before. It will all be hidden, so looks aren't critical here.
You can see a rough picture here:
http://carbuff.homeip.net/dash_install.html
I do recall wrapping after reading that again that I wrapped the outside with duct tape to keep eveything from coming undone. Maybe that will help. These weren't round to rectangular connections, but the idea is similar.
Good luck! Living in Texas, I understand the need...