Increasing width of raglan sleeves?

[wasabi]

I want to knit my first sweater that fits! However, my torso is about two sizes smaller than my hips and upper arms, and I'm not sure how to go about adjusting the sleeves so they are big enough without messing up the construction.

I'm planning to knit Morning Echo by Elizabeth Sullivan, which is a bottom up raglan cardigan. It already has waist shaping in darts on the front and back, so I'm just planning on adding in extra decreases on the side seams before the waist to merge the size for my hips with the size for my waist. I'm a bit stuck on how to deal with the arms though. Obviously I'll need to decrease more stitches up to the neckline (which is 2" for all the sizes), but I'm not sure the best way to do this. Do I just decrease at a faster rate? Cast off more at the arm hole? I've also read of the option of putting a dart on the shoulder, but I don't know how this would affect the fit/shape of the arm. Also, will I need to alter the armhole on the body? Will it need to be longer?

Any ideas? Anyone done this before?