I would like to be able to tell spaceclock to run some command when
I {single|double}-click it with {left|middle|right} button, more or less the
way that wmCalClock works.
See wmCalClock
http://www.dockapps.org/file.php/id/9
For example, I use this command-line with wmCalClock
wmCalClock -e ~/bin/xcal.sh
~/bin/xcal.sh is a little script to pop-up a calendar.