change the mouse pointer for window of one app

[Eli the Bearded]

I want the mouse pointer to change from my default left_ptr to
a different shape when in front of xeyes only.

How can I do that?

Here's what I've tried unsuccessfully:

1) setting the pointer with xsetroot (unsurprisingly it only sets
the pointer for the root window, not others)

2) Several variations on:

$ echo "xeyes*pointerShape: dot" >> ~/.Xdefaults
$ xrdb -merge ~/.Xdefaults

xterms respond xterm*pointerShape, but not xeyes.

3) An Xcursors theme:

$ mkdir ~/.xeyes ~/.xeyes/default ~/.xeyes/default/cursors
$ cd ~/.xeyes/default
$ cat > index.theme
[Icon Theme]
Name=Xeyes
Comment=Xeyes specific theme
$ cd default
$ for f in $(ls /usr/share/icons/default/cursors/) ; do
ln -s /usr/share/icons/default/cursors/dotbox $f
done
$ XCURSOR_PATH=$HOME/.xeyes/ XCURSOR_THEME=default xeyes

Nothing changed. I also tried an strace of xeyes, and never saw it
open any file in $HOME/.xeyes/

What else should I try? The goal, once I can figure out how to do it,
is to have an invisible pointer in front of a full screen xeyes window.

Elijah
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resorting to recompiling xeyes is cheating