About 6 months ago I heard about using "eyebrow trimmers". They work! I've actually attempted to slip up and it does NOT cut the fabric, but goes very quickly on the thread. The technique is to hold each side of the seam and stroke down the middle. Works for me. Bought mine in a package of three for less than $3 and gave two as gifts. You'll find them near the eyelash curlers in the cosmetics section at any big box store or pharmacy that carries that sort of thing.
Kay in NJ