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](https://microsoftteams.uservoice.com/forums/555103-public/suggestions/41022388-multi-channel-audio-usb-interface-compatibility)) , 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?)