sorry but there is no other ways of getting land besides the war and blocks,war is not so bad if you can get away with it,you have to get the claims first to avoid getting allot warmongering with either actions of spy's,spy's are much better fo this purpose because they have a higher success chance,then declare war,get the tiles with claims on them in the peace deal,if you dont have allot of money for armies get black market cooperation and other spy policies that boost the tax earnings ( i dont know if its a bug or not but the lower the tax rate the bigger the bonus is from those policies to the point that you actually earn MORE from lowering the tax than increasing it so get the tax range increasing policies too)

Ok, i expected something different. It's supposed to be economic victory, so i thought about target bankrupcy and paying debpts in exchange for land, or paying resources for land. It looks like it's undoable without serious army power :(