In my opinion a double pole "that has a gentler initial impact, then gradually increases pressure as you go fairly deep with upper body" does not have a place, ESPECIALLY for a weaker person. What you have to consider here is body position. I'm going to assume here that weaker means smaller build, and not just weak/unfit (for those, just get stronger eh?). For a smaller person, maintaining a good body position throughout the stroke is essential. This person cannot generate the large amount of force necessary to return the body to proper position fast enough to hold a decent tempo EFFICIENTLY.
With a long double with lots of effort at the end, you are forcing your arms back, your shoulders down, and your ass behind (but high) your feet, all defining characteristics of poor body position.
HOWEVER, if you initiate properly (notice I said properly, not powerfully), recover the hands quickly and WITH the body, your body position is maintained for the next stroke much better.
The reason I didn't say powerfully is that I don't believe this has to be a "power" thing. Most of the definition of this style is not in HOW MUCH power, but WHEN. The timing of this application has changed enabling efficiency due to improved body position. To do it like the world cup skiers takes crazy power, sure, but they can also do it properly at much lower intensities and speeds similar to that which a recreational skier is comfortable with.
Most athletes when coached properly will go into an 'old school' looking double pole with a long follow through on flats, but I can assure they are not gradually increasing the force, they are initiating.
As for training, this is 90% a technique issue, and 10% strength. Find someone who understands the new technique and can teach it well. For the next couple weeks you'll be sore, but not because it takes that much more strength, but because it's a slightly unfamiliar movement.
