splitting edge curves into pieces

In order to make a boundary blend, Iam creatingfirst direction curvesout of chains of edgesof the two shapes I'm blending between. The thing is that I would like to be able to break up the edges into smaller pieces sometimes and I do not know how to.


For example, let's say I wanted to make a blend between the top half of asquare and the top half of a circle.How would Imake curves that are only half the length of each of the two side edges of the square?


ps - The obvious chopping the squareand circle in half beforehand isn't an option in the case of what I'm actually doing right now, I'm just using the two shapes asexample to try to simplify things to get at heart of what I'm asking.

Use datum points at .50 or half way along each square / circle edge and then create sketches with these ? The BB can then use the sketches. Or you could make single sufaces and trim them using the datum points.