If I'm reading the fuse settings in MicroCore it should do that by default. Here they are for the Tools > Clock > 9.6 MHz internal osc., Tools > B.O.D. > 2.7v board setting:
The chip comes from the factory with the fuses set to divide the clock by 8. Did you do Tools > Burn Boorloader? This is required to set the fuses according to your selections in the Tools menus, even though there is no bootloader in MicroCore. Sketch > Upload Using Programmer does not set the fuses