This is a workout we have been doing a few times a month this spring and summer. After a warm up of running followed by some regular ski walking and striding on the hill (you can throw in some tire work or plyometrics here too if you want) put on the skis (we have found that the instinct to clean the snow out of your boot is sometimes too strong to overcome, so don't feel silly if you catch yourself scraping out the imaginary snow...we've all done it!)
We generally start this workout on the shallower part of the hill and do about 10 minutes of 30 second sprints, recovering by walking down the hill (skis still on, they won't glide much though). The second 10 minutes we move to the steeper part of the hill and do some shorter sprints up that.
The goal here is to forget that you are on grass and imagine you are on a steep hill in a race where there isn't much glide. It really does feel like skiing!
Depending on how long and hard you go, this workout can be pretty tough. It is a great way to work on striding technique as it is pretty hard to cheat and just run (as many people do when ski striding). We don't recommend using skis for every hard striding workout but it is good to do couple of weeks to keep skiing fresh in your mind!
Take a look at the pictures by Harry Nowell.