Efficient current drive with arbitrary waveform
What you have there controls the output current into the load.

You could replace the fixed 100 V supply with a variable voltage boost converter. This would be controlled by sensing the collector voltage on your transistor, driving it to (say) 5 V. 

You would choose the threshold voltage appropriately. A lower voltage means better efficinecy. A higher voltage gives you more headroom to cope with any rapid changes of the load impedance, or allows you to have a slower responding power supply.