Cubase tries to make sure you can’t set up a feedback loop in your routing, unless you can patch this physically with multiple ins and outs I don’t think you can do it.
Actually there are some free vsts that will allow you to do basic feedback…you might take a look at Senderella, but it’s not 64bit so no idea how the bridge or Jbridge will deal with it.
Also I don’t think it allows the 2 way feedback you are describing
Plogue Bidule is a more complex and paid solution that should do any routing you want…I think Blue Cat Patchwork will also do it.