The new channels/radiotray.py plugin allows to bookmark stations from Streamtuner2 directly to RadioTray (or now Radiotray-NG).

It'll require a patch for RT however, so it accepts the proposed DBUS request.

If you want to apply it manually, find /usr/share/pyshared/radiotray/DbusFacade.py and add following snippet:

   @dbus.service.method('net.sourceforge.radiotray')
   def addRadio(self, title, url, group="root"):
       self.dataProvider.addRadio(title, url, group)

Add it after playUrl or something. Just take care to keep it coherently indented.

I've opened a feature request #242 for this.

Same for RT-NG: #92, albeit this moreso requires support from the maintainers (not overly versed with C++).

See also the configuration options, on how Streamtuner2 maps stations onto RadioTray bookmark <groups>. Might need more work for Radiotray-NG.