rectangles sew together just as easily as squares. do not be scared! sew them end to end in rows then put the rows together. I would be inclined to offset the rows a little though. so on every other row, instead of beginning with a full rectangle, start that row with a half of the rectangle. then you do not have to worry about your seams lining up with you sew the rows together. or you could do a modified jelly roll race quilt with them. (google it. it's actually really easy, though may be a bit more cumbersome with only 5x7 rectangles. but still possible)