Hi and thanks for your question. You really don't need MIDI Bridge (although it might provide some functionality I'm not aware of). You can just use Virtual MIDI, which is built into MIDI Designer.
See this link. and also this link.
If you haven't bought MIDI Designer Pro yet, I strongly recommend that you try all this out with MIDI Designer Lite to make sure it does what you want how you want.
Comment back here if you cannot get this to work. THANKS!