Use the start up script in $SYBASE/$SYBASE_ASE/install to restart the primary companion without it being monitored:
startserver -f ./RUN_<server_name>
For example, to start the MONEY1 companion:
startserver -f ./RUN_MONEY1
If you use this script to start a companion server, it will not fail over when the server goes down, even if it is configured to do so. Use this method only if you are doing maintenance, and you are certain that you do not want the server databases to be accessible when the server is down.