Skintimacy is a board designed by Alexander Müller-Rakow, that allows to measure some conductance between one master and 4 slaves/players. It is designed with the idea of using it between 5 people touching each other, but the master and/or the players could indeed be objects.

This project gives you 4 MIDI controllers, each value depending of how much contact each player has with the master.

If you can get hold of one Skintimacy kit, it is a bijou.

Skintimacy website
Touch to MIDI interface using Skintimacy and Teensy project