1) Use the Unitize function to separate each face in the mesh and have them squarely fill the 0-1 UV space.
2) Select the edges where you want your seam.
3) Convert the selection to UV's.
4) Invert the selection.
5) Use the Move and Sew function.
6) Go in the option box for Unfold and select Vertical as your unfold constraint (horizontal if your UV's are oriented that way.
7) Enjoy your nice UV's.
https://www.youtube.com/watch?v=dahgVetfUZg
