You can use expressions about wherevere you have a text field.
So you can use expressions in the system condition "compare", in actions, etc...
I guess what you could use would be system: compare two values, put distance(0, 0, Sprite.Physics.VectorX, Sprite.Physics.VectorY) in the first field, and a comparison value in the second field (> 0 for example, would mean that the action would happen anytime your object is moving, since its velocity is not 0).