I highly suggest you just add an overflow tank. Frankly I prefer the clear plastic variety. Several side benefits. 1. You might save a dog's life by not leaving puddles behind. 2. You will run your radiator filled to the very top...adding coolant capacity and cooling ability. 3. You can check your coolant level at a glance by simply looking at the "cold" and "hot" fill lines on the plastic tank at any engine temp, and not having to open anything.

If you desperately need to maintain a pure stock look, a tank can be hidden in front of the core support beneath the airflow baffles. Universal plastic tanks available at every auto parts store for $15. And fancier/more expensive options are also available...