Adding real Fan to DELL Precision T5820

I have a DELL Precision T5820 and I want to add an exhaust fan at the back to improve the cooling for the system. I'm using a Xeon W2145, and it has issues with Limit Throttling, so I'm trying to improve its cooling. How can I add a rear exhaust fan to it?

I've seen some people use HD fan headers to connect the fan, but the problem is it always runs at full speed.

Does anyone have experience with adding an exhaust fan to this system? I'd appreciate any suggestions.

This is a picture I found of someone who installed it on his T5820.