Not worth it, and would likely just cause you more headaches.
Proper function of a catalyst relies on retaining temperature in order to burn the emissions. In fact, the O2 sensors rely on this temperature as well but they are typically self-heating. The usual upstream placement of the catalyst near the engine is deliberate, to allow the catalyst(s) to heat up quickly, retain heat, and lower emissions more effectively. If you relocate the catalyst further downstream you'll likely interfere with its operation - not catastrophically, but in a way that would make it slower to reach nominal temperature and possibly trigger a code by causing the ECU to think that it's functioning below the expected efficiency threshold. Furthermore, depending on where you were to place the catalyst you may end up with more heat transferring into the floorpan or baking something that shouldn't be exposed to that much heat.
Basically, if you're THAT worried about temperatures from your catalyst you'd be better off just improving your cooling system, running catless and/or getting that section of your exhaust ceramic coated to trap more of the heat inside the exhaust itself.