Resistor without terminals?
different conductive materials have a different bulk resistivity. so you could use them in this. eg get thimbles mage from or coated with conductive rubber in 4 different formulations (or the same formulation in different thicknesses) but the readings you get will to some extent be pressure dependent.

a better solution is probably to instead make a pad with many terminals
that are all fed to a single resistor via a diode network, that way even if each of the contacts bridges multipler terminals you can still read the single resistor







simulate this circuit &ndash; Schematic created using CircuitLab