1. Place Chest->StackInserter->EmptyGround in a row
2. Put 50 coal into chest
3. Remove chest
Inserter hand now holds 5 pieces of coal (you can check that by deconstructing inserter), and one piece of coal lays on the ground.
4A (minor bug). Place FastInserter over StackInserter (same direction)
Now you have fast non-stack inserter that holds 5 items ready to drop them

4B (funny bug). Place BurnerInserter over StackInserter (same direction)
Burner inserter turns around and fuels itself with all 5 pieces coal

Solution - extra items over stack bonus should probably go to inventory or spill on the ground when replacing one type of inserter with another. This is minor thing but may break things somewhere else in circuit networks or mods if someone assumes that under no circumstances inserter may hold more items than its stack bonus.