"I may rig an additional drain hose on the actual drain at the bottom of the cooler that runs back to the drain plug on the boat so that at the end of the day I can open that valve and let water drain directly out the plug of the boat."

This actually sounds like your best option, I don't have much experience in livewell rigging (only w/ kayaks) but using your existing drain for your boat requires no extra holes, you have endless options of different valves or connections to use that are removable.

The only other thing I can think of is to have another small pump inside the livewell to pump the water out thru a hose and down over the side of your boat, make it long enough to reach the water and no splashing??

Just my random thoughts.

Trev-