I think there might be an indirect way of doing it. (Fair warning before I continue: I have no idea if this will work. I have no experience with PC UTAU, so this is purely theoretical. I did some research on PC UTAU to compare, but that's it.)
That being said, here's my suggestion. From what I can tell, the key difference between the way the PC version stores VBs and the way Synth does is that Synth requires the voicebank be in a single .utauvoice file and in the PC version you move the folder containing all the required sound/files into the "voice" subdirectory of the program. It seems to me like what might work is if you made it into an .utauvoice file at first. Then you would go into Finder and right-click on the file and select "Show package contents," then copy all of those files into a folder. Then you'd compress the folder and send it to your friend, who should be able open it (the only problem I could see with this is if they didn't have software to open the file, but it's possible to decompress files online or convert it to another compressed folder file extension, so it's easily fixable) and drag it to the subdirectory.