Is it possible to increase travel on Cannondale Scalpel?
If you get a fork with longer travel, it'll result in a less-steep head tube angle, and a higher BB. I'd say it's worth trying, but in your case there is a major complication: the Lefty fork. So you have two options:


Get another Lefty with longer travel. And I don't think they sell those separately, so that's probably impossible.
Get a normal fork. And this will means replacing the parts that are designed to work with the Lefty: the front wheel, the stem, and the headset (you'll have to get a special reducer headset to make it fit in the over-sized headtube.) This is definitely doable, but you'll be better off just buying another bike.