I have not seen it every in any version of power2go. I would say you could just try a different burning software unless some that knows more answers your question about power2go. It's been over a month since you asked and nobody came back that's a good bet it is not supported.
Try google for imgburn and give it a shot. This is not an endorsement for that software just a straight forward acknowledgement that it will burn blu ray and 2 at the same time. I would caution you though. Burning 2 blu-ray at the same time can be system intensive so there are some things you have to check and make sure before doing it. System resources and so forth.