If it's just 1/2" x 14" rectangle, then its not a job for a coping saw. For a straight cut that long on stock as thin as 1/8"' I think I'd probably put the work piece flat on a waste board, clamp down piece of angled aluminum for a straightedge and score it
deeply with a utility knife. Leaving the straightedge in place, I'd finish the cut with the razor saw held almost parallel to the face of the board. Double sided tape can be useful for holding the straightedge down if you don't have a clamps with deep enough throats.
If its a curved shape I'd use a fret saw, support the piece across two closely spaced boards, and take a
really long time to make the cut -- except that I probably wouldn't try to cut a long narrow profile from 1/8" plywood with hand tools. I'd use an X-acto to cut multiple copies from basswood or balsa and laminate them after they'd been shaped.
With that saw (that's the 32 TPI blade from the
Zona 4-in-1 kit) I would not try a 14" long cut the way I did it in those pictures. But with a straightedge -- should be doable with a boxcutter and an X-Acto razor saw (if that's what you have). Or just with the utility knife, if you don't mind a little splintering on the back side. It'll be time consuming, but doable.