At this point there are two approaches to achieve this. One is using pt-kill from Percona Toolkit, and the other one is to use a bash script with a lot of pipes :)
Why would someone use the second approach? I don't know, perhaps because there is no Percona Toolkit available.

[codesyntax lang="bash"]

for i in $(mysql -e "show processlist" | egrep -v "system user" | grep '^[0-9]' | awk '{print $6" "$1}' | sort -nr -k1 | awk -v threshold="60" '$1 > threshold' | awk '{print $2}'); do mysql -e "kill $i"; done

[/codesyntax]

If you can/want to use pt-kill and don't know how, please read this.