I got an aqua computer Quadro in my build and it runs off a USB header and has 4 temp sensors and 4 fan headers. Other option is to use motherboard temp sensor (a lot of ASUS boards have this). And finally a low tech option is something like this. But yeah, at that point you just have to set the speed of the fan fixed so it's high enough to keep load temps under the danger threshold or have some sort of manual fan control.
That's a cool little unit and given that I won't be using the internal USB header any longer in the new build, I could definitely go this way too. So just hook up the sensor, 2 fans and the USB header provides power as well as data? Or is the molex connector also needed for power? Then just set a curve with the software based on coolant temp and that's it yeah? Where would be the best place to mount it in the case do you think using double sided tape?