I'm just thinking, if these cannot be used together with eg. velox's backing plates (basic kit, w/o inlets & hoses) connecting via some hose? As in - what diameter outlet of rooducts is and to where it points?

I have some sort of abomination mix between APR and Velox kit for my brake cooling. It is totally possible to have something patched up together to get the air where you want it, from where you want it. Using duct-tape to in increase the outer diameter of a hose to make it fit tight inside a bigger one is suprinsingly sturdy (as are zip-ties).

RooDucts
 

Sorry I do not have a photo of them installed. You can go to rooducts.com and see a picture of one installed. Although it's not a BRZ, it's very similar.
But from these pics of mine on the bench (sorry I couldn't figure out how to get them right side up), I think you'll get the idea. The inlet is on the underside of the LCA with the output nozzle wrapping up and around the backside of the LCA and pointed at the hat area of the rotor. The output nozzle has to be tucked in tight to the LCA so it doesn't interfere with the tie rod at full lock--that's the reason for the trapezoidal shape.
Circumference of the output nozzle is about 7"--maybe equal to a 2 1/4" round hose.
Like Icecreamtruk, I don't see why you wouldn't be able to connect them to a hose but you should check with Randy at RooDucts.

The duct outlet has a hard time fitting in the space between all the linkages and the tire. The reasoning is that the duct causes the air inside the wheel to "churn" and doesn't just stay stagnant, ever increasing in temperature. Gearhead's data and results show that, for whatever reason, they work.

https://i1.wp.com/rooducts.com/wp-co...00%2C225&ssl=1

https://i1.wp.com/rooducts.com/wp-co...91%2C300&ssl=1

https://i0.wp.com/rooducts.com/wp-co...00%2C295&ssl=1

https://i0.wp.com/rooducts.com/wp-co...00%2C146&ssl=1