It is a good question, as there doesn't seem to be a way to disable the StaticBody2D node itself.
My workaround was to turn on the "Trigger" flag on the child CollisionShape2D. This will have the effect that kinematic and rigid bodies can pass through the static body. As the documentation states "A trigger shape detects collisions, but is otherwise unaffected by physics".
Just turn this flag on to disable physics. For example, assuming you have a child CollisionShape2D to your StaticBody2D node, a script on the StaticBody2D would do something like:
var cs = get_node("CollisionShape2D") # get child collision shape node
cs.set_trigger(true) # turn the trigger flag on to disable physics