No, you need to get a pressure feed. Can't just put a line into and out of the pan as the pan isn't pressurized.
Doesn't your car already have a tranny cooler built into the radiator? If so, you could pull the return line off the radiator cooler, send it to the auxillary cooler, then hook the aux cooler output up to the return line to the tranny.
So you'd then have it go out fron the tranny to the cooler in the radiator, out from the radiator cooler to the aux cooler, then out from the aux cooler back to the tranny.
Did that on my truck and it worked great. Keeping the radiator cooler hooked up makes sure it doesn't get too cool. You do want the temp to be warm, but not hot.
Cosmos Black/Black 1995 540iA M-Sport
BMW Individual Exclusive Edition, 1 of 65 total, 9/25/95 Build