NOTE: You do this at your own risk. I am not encouraging you to do it, and neither is Club xB. This is merely a guideline. Hope it works out for you.
I was tired of not being able to close the center vents, so I replaced them with some that could. My girlfriend is constantly freezing and I could sweat while naked in an igloo eating Otter Pops, so this was done for her.
This is a slacker DIY. Wear Safety Goggles, get some gloves, don't shoot your eye out, you break it you bought it.
Tools needed:
03-04 Mazda 6 Dash Vents
Dremel
Either a small screwdriver, or Heavy Duty dykes/pruning shears.
I bought this on ebay:
Its the 03-04 AC/Heater vents from a Mazda 6.
There are tabs and stuff you can use to ensure that everything comes apart normally.
If you want to use that method, i found this:
Mazda6 / Atenza > How To: Boost Gauge Install (Stereo Vents)
Or, if you are like me, you can get a pair of heavy duty dykes or garden shears, cut the outer stuff to make it crack, peel it open and throw it away.
Grab a dremel with a grinding or very coarse sandpaper head and make the edge flush and smooth all the way around.
slide into vent slot. it sits flush in the whole.
It turns but it sticks a little, i am sure a little finessing with the dremel could remedy it.
Here is the final product:
