Master switch in stack needs to stay the same

Hi,

Hope someone can help with this.

We currently have 7 Powerconnect 6248 switches stacked. These are connected using fibre to a datacentre 500 yards away.

The fibre connection to the switches in the datacentre is connected to the interface on the master switch in the stack.

When we need to reboot the stack for any config changes the master switch could change and we would need to place the fibre connection into whichever switch becomes the master and change some VLAN config.

Is there a way to hard code the stack to always choose a particular switch as the master.

My gut feeling is MAC address but need to know for sure.

Thanks is advance

Steve