More digital I/O pins for pixhawk

Hi!

I’m looking for a way to quench out more digital outputs/inputs of my pixhawk 2.4.8. I’m using a wheel encoder, brushed motor controller with relay and additional GPIO peripherals and running out of pins.

I found in “libraries/AP_HAL_ChibiOS/hwdef/iomcu/hwdef.dat” that the main PWM outputs have a GPIO definition as 101-108, but I guess that’s specific to the IOMCU only?
Is there a way to (ab)use the main servo outputs for digital i/o?

I found that I can use various pins as GPIO when modifying hwdef.dat (like UART8_RX/TX etc.) but it would be better if no firmware patch would be needed and, even more important, pins from the DF13 connector would be better.

Or could I maybe use pins from expansion hardware (like PCF8574 for i2c or something similar) for additional switches or relays?