Using neighboring traces for PCB return current
With the 20kHz being the max PWM, the frequency is low enough to not be a concern. FCC limits don't apply until 1.7Mhz and the harmonics will likely stay below that value. 

If your worried about mutual inductance between trace loops on your own board, then make sure you keep the loop area small, as to create smaller inductors. 

At 1Amp a 200mil long conductor will need to be at least 13mil wide to keep the temperature delta below 20C

Take care to not 'chain' traces (this is just an example and not the full h-bridge of a BLDC controller):







simulate this circuit &ndash; Schematic created using CircuitLab

Each trace has resistance, this can be calculated, make sure you take this into account as small resistances can add up.