setInterval with prototypes

I have a movieclip prototype which I want to be applied to different movieclips every so often. The prototype controls it’s movement, when it runs, the mc eases to a random x and y and stops. After that I want it to keep executing that movement prototype over and over, ie, keep moving around.

I know how to use setInterval with functions, and I know movieclip prototypes basically are functions, but how can I get setInterval to work with movieclip prototypes assigned to specific movieclips?