Core for standalone ATMEGA32U4?

I have a custom PCB with the ATMEGA32U4. I have no oscillator, and did not breakout USB.

I broke out the MOSI MISO SCK RST pins though.

I can't find a core for ATMEGA32U4 that exists without an external oscillator. Can I massage an existing core to let me choose internal 8 MHz?

Thank you for your time.