The ornamental design for a mount under bench/bleacher cup holder, as shown and described.
FIG. 1 is a front perspective view of a mount under bench/bleacher cup holder showing my new design;
FIG. 2 is a left side elevational view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines showing the mount under bench/bleacher cup holder in FIGS. 1-3 and FIG. 5 are included for the purpose of showing environmental structure and form no part of the claimed design.