I saw another idea here for a continuity tester which has much lower thresholds. As designed  it is hard to tell the difference between 0Ω and about 20Ω or so, rather this is optimized to measure 100Ω to 2kΩ or so.

So, perhaps, a range switch to go 100x on the bias current, 40µA to 4mA. 

I will be thinking on this ........