It is possible. Basically you install a rack and put the dryer on top. Then you put the washing machine at the bottom on a roller or coaster. You'll have to be creative with the wiring and the water inlet/outlet. Basically, you want to make sure you can pull the washing machine forward without disengaging the power wire, or the water inlet/outlet pipes.

As for the dryer, usually not an issue, but you need to make sure you can service the lint filter yourself. Don't let it accumulate, it will become fire hazard.