Sure! It’s a bit complicated at first and using linked racks is way more easier, but since I was not aware of this function before (it was quite a busy time before the gig and I had not the chance to check out every detail), I used this technique.
First you need to go into options, misc and activate the loopback ports and also (I don’t think if its necessary…) “show environment audio[…]in racks”.
This procedure works also the other way around:
Go into your backgroundrack and load the desired instrument. Let’s say FM8. Now go into options and open the MIDI ports menu. Create a midi input called FM8 (or whatever you want) and do not assign any physical MIDI input to it. Now go to the audio ports, create a new stereo input (!) port and call it “Audio FM8” and do not assign any physical audio input to it.
Close the options window and open the input routes of the background rack. Set up a new route from the new created FM8-MIDI port to the input of the plugin. At the plugin choose “Loopback - Audio FM8” as output port.
Now close the background rack and go into your song. Open the route menu. Create a route from your mainkeyboard to the “Loopback - FM8” MIDI port. Create another route from “Audio FM8” to your Main Outputs.
Done!
It sounds quite complicated but it works perfectly. Anyway: I’m really with Torsten. Using linked racks is a better method for that.
//edit: @Torsten You wrote that it would be nice to have midi and audio ports of the BR available… they are if you do it like this. But of course depending on how many different plugins you want to use you can easily loose oversight.