This already exists see:
http://docs.cloudlinux.com/index.html?configuration.html

<!-- killing slow SELECT queries (no other queries will be killed) -->
<!-- if "log" attribute was set all killed queries will be saved in log file -->
<slow_queries run="on|off" log="/var/log/dbgovernor-kill.log"/>

and
<!-- Time to kill slow SELECT queries for account, can be different for accounts in seconds -->
<!-- enabled only when slow_queries run="on" -->
<limit name="slow" current="30"/>

+1