Hello again,
By "biasing the LED" i mean you connect a large value resistor from the mains right to the opto LED. That partially increases the voltage so that when the normal sense resistor voltage increases it can exceed the LED voltage and turn it on and hence turn on the opto.
So say the LED turns on at 2v. If it was biased to 1.5v, then when the current goes through the sense resistor (1 ohm) the voltage generated there pushes the LED voltage up higher above 2v and turns it on. As i said though it's not that accurate either.
I like Ron's idea too though. If you can spare a transistor you should get decent operation with that fix. However, beware that you must also derive the +5v supply from the *mains* voltage NOT from the circuit or else you'll loose your isolation which i assume you wanted because of the opto being there in the first place. So you need to build a little power supply (diode, filter cap, etc.) for powering the LED, and it should get it's source voltage from the mains supply, unless of course you dont really need isolation.
In any of these solutions you should also be aware that the opto will pulse on and off unless you filter the input or output.