Whenever I use livestream to do my live Reason broadcast I have a work around that works. Livestream has a similar issue where it only detects the input of the 2i2 (I own the same audio interface) so I know exactally what you are talking about.
Here's what you'll have to do.... You'll need a seperate mixer, a stereo 1/4" to mono L&R, 4 1/4" cables.
How to wire it up. Plug the stereo 1/4' to mono L&R 1/4" into the headphone output, connect 2 1/4" cables to the mono L&R and the mixer, plug your mic into the mixer and wire the output of the mixing into the output of the 2i2.
It's quite a workaround but it was the only think I could think of. If anyone has a better solution I'm all ears. I'd love to take the mixer I bought back and get my money back if I could.