AC/DC

If the DC is unipolar, just put a diode in. It will conduct the DC and (half) the AC. The capacitor needed for AC will not adversely affect the DC.

As to the arguments above re power disappation, if you are going to drop 215 Volts, you will generate heat.

One possible solution (I have not thought this one through) but what about enabling the circuit only when the input is sensed, that way you could achieve enormous energy savings. I am thinking of something line an optocopupler driven by an output to enable the constant current generator, the current generator then drive another optocoupler for an input.

Erik