I seem to remember a document released early in the US release of the Dreamcast talking about how Yamaha had developed the method to write a gig of information to a regular CD-R and this is, of course, the standard that Sega adopted (this is all from memory btw, not exactly sure of the details or even if the information is valid from a good source), but around that same time another software company had discovered a similar way to store about a gig of data using the yamaha burners. Apparently there were certain models of Yamaha burners that could be used in conjunction with this software to burn GD-ROM compadible discs.
I believe there are several sources that cite that the GD-ROM burners were essientially a somewhat common Yamaha burner used in conjunction with a set of software, one set created by Yamaha, another set created by this other software company. I'll have to see if I can't dig this document up for those who are curious. So if you are able to obtain this software, theoretically (if this document was true), making GD-ROM discs is possible.