I've done a little research and found that the Sharp PC900V opto only needs a little more than 1mA to work. This little beast has some electronics built in so it is fairly sensitive. I also have some on hand as I use them in another project.

So, with half wave and reduced current requirement - the dissipation is decreasing! I dare say a simple constant current circuit may prove to be the solution. Now I have to select a suitable high voltage transistor that is easy to get!