A venturi version could be possible, with a little bit of modification of a few fittings.
What comes to mind quickest is a 1-1/2" tee, with a 1/2" or 3/4" side inlet. grind out the stop shelf inside the side inlet, so you can push the 1/2" or 3/4" all the way into the flow area. Cut the small pipe at about a 45* angle before you glue it in, with the open end of the pipe towards the outlet.
Might work, but you will have to experiment a bit to get it right.
If you know the approximate flow rate, you can use Bernoulli's equation to find the pressure difference.
http://www.efunda.com/formulae/fluids/venturi_flowmeter.cfm
But my guess is that it needs to be much narrower. A spa jet is maximum about 7/16" orifice for a 1 1/2" pipe. Why not just use a spa jet venturi tee?
Maybe more like this?
View attachment 32749
1 1/2" to a 1" reducer, 1" T pipe and back to a 1 1/2"
Will the reduction be enough?