Multiple grid.appScope calls when used in cellTemplate

I want to be able to display the result of function in a cell and for this I've used grid.appScope as per the plnkr example found at http://plnkr.co/edit/xlnjrtpg9EuL0nOG1cZy?p=preview.

I noticed the $scope.myFn function is called 60 times for the first load of just 10 results and when you scoll the grid up and down the function gets repeatly called 1000s of time (you can see this in console).

In my case, I want the grid.appScope function to get data from an $http request which becomes problematic with the repeated calls.

Is there anyway to prevent the mutliple calls so each cell calls the grid.appScope function only once?

Are there any other solution other than using grid.appScope?