Bluetooth dongle default for Mac Mini

I'm looking for a script that will make sure that my bluetooth dongle (Broadcom, sitting in my Apple wired keyboard) is the default for my Apple mouse. I use the Host Controller Selector in the Apple Bluetooth Explorer to select it - but after reboots (or power outages like last night) it often switches back to the Apple BRCM in my Mac Mini - which unfortunately is completely useless and makes the mouse have lags and poor range (that I believe is a know issue and AFAIK there has never been a fix). Everything works fine with the external dongle but I can't set it as default. Tried to write it in Apple Script but that doesn't seem to go down to that level.