I claim the ornamental design for a cat scratcher insert holder, as shown and described.
FIG. 1 is a perspective view of a cat scratcher insert holder, showing a first embodiment of my new design;
FIG. 2 is a front elevational view of FIG. 1;
FIG. 3 is a rear elevational view of FIG. 1;
FIG. 4 is a right-side elevational view of FIG. 1, the left-side elevational view being a mirror image thereof;
FIG. 5 is a top plan view of FIG. 1;
FIG. 6 is a bottom plan view of FIG. 1;
FIG. 7 is a perspective view of a second embodiment thereof;
FIG. 8 is a front elevational view of FIG. 7;
FIG. 9 is a rear elevational view of FIG. 7;
FIG. 10 is a right-side elevational view of FIG. 7, the left-side elevational view being a mirror image thereof;
FIG. 11 is a top plan view of FIG. 7; and,
FIG. 12 is a bottom plan view of FIG. 7.
The broken lines showing a cat scratcher insert on FIGS. 1 and 7 and four legs on FIGS. 1-4, 6-10 and 12 are for illustration only and form no part of the claimed design.