you could remap some of the other pins (UART,SPI,GPIO) to
PWM output since most of them have timers associated with
them (I recommend having a look at the Lisa M schematics).
That should give you enough ouputs. Indeed it would be at
3.3V logic, so you would need some voltage converter to
make it compatible with the servos/ESC.
The drawback is that you would have to sacrifice certain IO
depending on how many extra outputs you need. The software
side should be pretty straightforward, you would just have
to define extra PWM outputs in the board files.