Here's an idea... I haven't tried this myself just yet, but I'm pretty certain it would work.
Create 2 scripts - startbigclock and killbigclock
In startbigclock, do
/nto/bin/BigClock -a 0x40010004 -b6 -m3
echo "$!" >/tmp/bigclock.pid
and in killbigclock, do
Note : It's critical to use ` <--- backticks on the pid=... line. That will substitute the content of the file into the pid variable.
So, in a nutshell, save the process id of bigblock, and then retrieve it and kill it. All you need is to make your web scripts invoke startbigclock and killbigclock and you're off to the races.
Let me know if that works out for you.