Just use a small positive feed-back (a high-value resistor from output to noninverting input and a low-value resistor from there to gnd) and input the referencs (threshold) voltage to inverting input.
You may need to consider that output swing is negative (if you have dual power supply) and also that your positive output may be higher than your receiving parts really needs or wants. A simple resistor/zener takes care of that.
