Using Andrea's idea of a no-screw tieback, I designed this one, which is a one piece deal instead of two. It's just a rounded rectangle with a hole in the middle, then heated and bent to make it curve on the front and back.
I hope you can see the thing in the pix, but it's easy to use and is still fairly invisible. It does change the shape of the curtain, so I'm not sure if I like it better than the first design that had to be screwed to the window moulding (an idea my husband does not like!)
cheers, dee