Holding thread wires = training for Olympic level shadow puppet competitions. Clay isn't cheating or amateurish. Play-Doh might be.
Press thread wires into the clay blob a short distance, using the unsized threading job as a 'guide'. A plus, it'll stand them up between measurements, instead of losing them in the chip pan.
Bigger diameter? Use a popsicle stick/ tongue depressor + clay, or styrofoam panel from packaging fresh meat. Good reason to not have a houseful of vegetarians.