I use these - not this exact one, but lots of very similar out there.

http://www.ebay.co.uk/itm/Curtain-Ho...item35c579e13f

They DO mark the film/paper as they have a strong grip, however you can grip with 1/8" - 3mm of contact so the contact point is well outside the image area. I also clip one at either corner of the hanging negative strip to keep it straight.