You'll likely need to make an event handler for a unit move command. Assuming for a moment the unit is always sliding towards the angle it's facing, your event handler might look something like this:
- Event - Unit Is Issued Order - Move
- Target Point = Target of Order - Triggering Unit - Index 0
- Issue Order - Triggering Unit - Stop
- Make Triggering Unit Face Angle over 0.3 seconds - Angle between points - Position of Triggering Unit - Target Point
That's a very simplified version of what I've done for ice physics in my own map. Instantly telling the unit to stop prevents the actual move command from doing anything, then turning the unit via a trigger gives it a nice smooth animation.