Sending audio from one tab to another?

Is there any way to send the output of audio playing in one tab to the input of a track on a different tab? I can do it by patching my soundcard back into itself, of course, but it'd be nice if there was a more elegant way to do it within Reaper maybe using rearoute somehow. Any ideas?

All I can think of is that it might be possible to spawn two separate instances of REAPER rather than project tabs and then try ReaRoute. But I'm thinking out loud here, never tried doing it, don't know if it would work. Good luck and let us know how you get on. ;)

Doesn't seem to work ... you could try using Virtual Audio Cable maybe?