I think the Autospeed one is very clever in the way it works.
They have identified that the intercooler is a heat sink first and foremost.
They identify that the inject pulses are the key to showing how much the car is being driven.
I think the only other way to do it would be to use an inlet and ambient sensor as mentioned above.
But you have to add a switch off also.
Imagine a thrash around the track, you heat soak your cooler.
Then you park it and let it cool down. The heat sink is going to be transferring it's heat back into the air flow, and surely the temps will be high enough going into the inlet.
You would want to cap the sprays at maybe 2 seconds every 10 when the AFM is low, otherwise you will end up with a wet intercooler which isn't really doing much cooling as the water heats up and insulates the heat.