I was fortunate to have my own clientele during my Summer breaks (and weekends if I wanted to score some easy work). We noticed a small box of several wires, including a brown one. We snipped off a length, yanked the wire out, then cut the sheath so it was basically a brown tube, but of the right size such that we could cut it into pieces - enough to look like mouse turds. We spaced them out so it wouldn't be blatant, just enough to lead off one side of the desk and under a stack of paper