I have no advice for you. But your post prompted me to google the race where I saw a chart showing the elevation: I wonder if there are many places in North America that could provide a decent training ground for a climb of that magnitude and duration! Beyond putting 3 bricks under a treadmill, or running a lot of stairs in high-rise buildings, I'm not sure what I would do. Good luck with this: definitely not a challenge for a humble beginner such as myself...

You don't need the highest setting on the treadmill. Training at an average incline of 6% (4% for the average elevation of the Jungfrau + 2% just for using a treadmill) will be plenty. You could also vary some stretches in the 2-4% range with some distances around 10-12% (which seems to be the steepest the course gets).

You will have to put in some hill repeats, there's no question about that. Races such as the Whiteface Mountain Uphill Footrace (early June each year) are great practice (8.3 miles @ 8% incline in usually hot and humid weather).

And being in Nova Scotia, you have great training grounds for long weekends: go to the Highlands Nat'l Park. If you can handle those hills for a 20-miler, even the Jungfrau won't be that radical of a challenge. The hills there are not the same steady incline, but they are steeper and repetitive.

Have fun. I may see you there one day.

Take care.

Mars