When using a coping saw, I sometimes find it easier to saw with the workpiece held vertically. The birdsmouth vice shown here positions the workpiece at a comfortable height for sawing.
The drawings above show how it goes together. The base is grooved to hold the vice face. I cut a large V-notch into the face of the vice to provide clearance for the saw blade as you cut. A pair of slots provides adjustment for the clamp. I fastened the clamp with pairs of coach bolts, knobs and washers.
To use the vice, simply secure it to your worksurface. Place the workpiece between the clamp and face then tighten the knobs.