There are several options, depending on how much room you have, where the leak is, etc.
Depending on access and the OD of the line, you may be able to replace a segment of the line with rubber hose. You can buy transmission cooler rated hose at any auto parts store (do NOT use any other type of hose). Cut out the bad segment with a small tubing cutter, add two high-quality hose clamps at each end and you're back in business.
I've also used a piece of transmission cooler line to bypass leaking transmission coolers temporarily, just as a way to limp home, but this is also a great way to overheat the fluid in warm weather.
Not sure whether JB Weld or repair tape would do you any good.