Blocking sweater sleeves knitted in round

I'm working on a child's cardigan pattern that has a turned hem on the skirt of the sweater and on the sleeves. The turning row is K2tog, yo. When I block the sweater, I want to emphasize this row, so that it creates a scalloped edge on the hem. I plan on using the string blocking method (stringing a piece of cotton yarn or thread through the row and putting tension on it to keep the row straight while it dries). This is the first time I'm trying this method, and I'm not quite sure how it will work on a hem knitted in the round (the sleeves). My plan is to put half of the sleeve on one thread and the other half on a second thread. Does anyone know if this will work, or does anyone have any other suggestions?

Any assistance is appreciated.