I've just tested the getftargs opcode with ftgen and it seems to work fine, but let me know if it isn't working for you and I'll see what I can do. In the end we can always ask John at the Csound list.
By the way, it would be great if the mode property of the filebutton in Cabbage 2 would accept -instead of "file"- the arguments "open" and "save". Right now it triggers an "Open file..." dialog and we would need a "Save as..." one in order to give getftargs some use. Of course you could always end up generating the file name in Csound with the current time stamp or similar, but that's cumbersome to manage afterwards.