/melee on sneak=on hide=on
then
/melee save
OR to disable
/melee on sneak=off hide=off
/melee save
Alternatively, as toric225 said, you can edit your ./charname_server.ini file and then /melee load.
NOTE: This solution uses MQ2Melee rather than KISS so it will be in effect even when KISS isn't running. If you are looking specifically how to do it using only KISS and not MQ2Melee, that's a different question entirely. But I believe this answers your question.