I was also hoping to make this possible, but it is not due to a design decision Electrosmith made with the seed. The codec they used has a digital high pass filter on the ADC side which cannot be disabled in software. I made mention of this a while back here:
I’m currently waiting on my second revision PCBs to be delivered. I hope to populate and test this revision in the coming weeks. If all goes well, I plan to offer a few DIY kits with parts and through-hole only soldering soon after. I’ll be updating this thread with my progress, so stay tuned if you’re interested.