Tailstock pressure pad.

[Toolmaker51]

When pressure alone won't suffice, there are hardened 'grippers' that drive parts. Grinding and finish turning also use 'face-drivers', exactly like woodturners do, just indenting the surface at each end. Otherwise, the process is identical to olderdan's pressure plate.
Workholding & Positioning - Fairlane Products
Which reminds me of face turning flat gaskets and seals. You can rubber cement material to plywood, or clamp as olderdan describes. Plate does need to be close to intended edge, cutter is simple as a pointed X-acto or scalpel held like a boring bar. If doing several, cut one side of all, then use that as a register for the other cut.