I have a pile of squares next to my machine and I use them for leaders and enders...Bonnie Hunter's method. I can easily make a bunch of 2, 4, 9 or 16 patch blocks this way while I am making another quilt entirely! When I am putting the 2, 3, and 4 patches together to make the block, I finger press the seams to one side (making them opposite for the other piece), cuddle the seams together with my fingers, pin the seam and sew. Usually end up with a decent match up...but there is always my seam ripper handy if it is off too much!