I have been investigating this over the past few days as I was intrigued to see if we could set the sim state on the aircraft as Umberto suggested. Unfortunately its bad news, whilst you can set this flag on the aircraft it does not fix the issue.
It would seem that this is an underlying simulator issue where the velocity vectors are being continually calculated when the aircraft is frozen by GSX. These values are what vatsim / multiplayer are using to create the smooth animation we see between each update.
Here is a picture of the CRJ resting on the tug whilst there is no movement, notice the velocity vectors and also reported speed.
Not sure where the fix lies, probably with Asobo but its possible that the vPilot guys could change how they predict motion when aircraft are on the ground.