This drink doesn't stand up to dilution very well. That's why I call for a quick shake and a half ice-filled Collins glass. You want to shake vigorously because the cream of coconut can be difficult to mix, especially when it gets cold.
This recipe comes from the Soggy Dollar Bar on the island of Jost Van Dyke in the British Virgin Islands. It is called the Soggy Dollar because they don't have a dock, so if you sail to the bar (many people do) and don't have a dinghy, you swim in and pay for your drinks with soggy dollars.
You can usually order Painkillers as a number 2, 3, or 4 which corresponds to the number of ounces of Pusser's in the drink.