For what it's worth, and I'm probably wrong but, I don't think your worry about the opto is properly directed. I think the concern should be placed on the PIC. If you don't have the flyback diode on the relay the back EMF will be rectified through the opto into the PIC. The reverse diode in the opto will not dispose of the relay field collapsing only rectify it to the PIC. You stated the diode on the relay is there so IMWO the diode drawn across the opto is unnecessary.

I would appreciate it if when the real engineers tell me I'm wrong that you do it gently.;-)