Hi riverrat.

I'd suggest floating fast growing plants in the tank. They'll add to the biomass and also block out some of the light. That should go a long way towards deterring algae growth. If you do this, you can dose like normal, perhaps not quite full blast Ei but as long as your plant mass is high you'll be ok. As the HC roots and sends out runners you can begin removing the floating plants a little at a time until you eventually phase them out.

This really is easier than trying to balance a sparsely planted tank on the head of a pin.