The ornamental design for a cooler mounted holder, as shown and described.
FIG. 1 is a front, perspective view of a cooler mounted holder showing my new design being mounted on a water cooler. The structure shown in broken lines is for illustrative purposes only and forms no part of the claimed design;
FIG. 2 is a top view of the cooler mounted holder of FIG. 1;
FIG. 3 is a front view of the cooler mounted holder of FIG. 1;
FIG. 4 is a bottom view of the cooler mounted holder of FIG. 1; and,
FIG. 5 is a side view of the cooler mounted holder of FIG. 1.