How can I mix multi-channel input device down to mono?

I have a microphone and Soundflower installed, and an aggregate device set up in Audio MIDI setup to mix the two together. My mic has two channels, and Soundflower has both a 2 channel and a 64 channel device. I just put them all together.

The problem is, I'm trying to use this as a "mic" input for Microsoft Teams (which does not support multi-channel input audio), which seems to only use one channel. With the settings as my screenshot shows, people can hear only my microphone; but if I swap the order of the devices so that Soundflower is first, people can hear the Soundflower output, and not my mic.

I'd like to mix these channels down to a single channel that I can use as the mic input. Is this possible (without external hardware?)

Been a while since I have played with Audio Hijak but I do believe it may do what you need it to do, and a lot of other audio tricks handy for people who do podcasts and audio mixing, though not for free.

https://rogueamoeba.com/audiohijack/