If the HSTs are fairly small, see if this would work for you. I have the green tape aligned with the needle (not needed for this) and the red one at the 1/4" mark.
This way there is no need to draw the diagonal on the fabric. Line up corner to corner on the red at the "bottom" end and with the outside of the 1/4" foot at the top. Go ahead and sew, turn it around, line up again and sew, then just cut through the center. ( I do realize that this may not work for all machine set-ups, but lucky me!)
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