FWIW I recently installed a bypass valve and happy with the results. This is the valve I used:
I looked at the coolant routing on the v10, and decided I didn't want to spend the time to truly understand it. So I just went with the bypass rather than something that blocks flow completely.
I attached the vacuum input to the max AC recirculation door. I may yet hack something up for the vent setting, but honestly I can also just run the AC for that case. I generally don't mind the drying effect.
Somewhat ironically this is directly related to installing the agile valved fox shocks. At 75 mph in 114 degree weather the ac vents were blowing 75 degree air while the van was much warmer than that inside. Coolant temp was at 220(+?) degrees. Slowing down helped, and before the shocks I would not have been driving that fast, but now that I can....
I've not been back out on i5 on a hot day yet, but I've seen a huge drop (10-20 degrees) in vent temperature in other situations, even fairly hot ones.
Total install time was about an hour. Edit: I needed exactly 5 feet of vacuum hose, I'd buy 7 feet if I did it over. Routing through the fender, above the fender liner and in right by the fuel cut off switch is pretty simple. Put a pan under the van, I lost about a half gallon of coolant just cutting the lines and being quick with the connections. I didn't have clamps big enough for those lines, so I did it that way. Worked fine, but the coolant is under a little bit of pressure there. Probably just from what's in the core and above it, but it gushed both ways.