A little late now, but you can install the sender in the pressure test port on the side of the trans.

Careful with this one. I know with Ford's EDO4's, the test port is a poor choice to pull temps from. Something about the fluid is not in full circulation and the temp reading does not reflect the actual state of the tranny. In the output line to the cooler really is the best place. It should be the hotest fluid available.

Michael