Use Communotron 88-88 as attachable part and Oscar-B Fuel Tank as target. When part is just pulled out of the inventory it attaches with no effects. When it's moved it triggers momentum on attach. The amount of momentum is different depending on the target parts.

This issue is in fact even more severe. Due to KSP logic every part that is being moved becomes physical even though it's set physicsless in the config. It happens because detached part (or assembly) is transformed into a separate vessel which cannot be physicsless. It's one of the reasons why effects show up.