I finally figured out how to get the LimeSDR Mini working, and I'm writing it down here so I don't forget how, but also so I can get upset later when I try this again and it doesn't work mysteriously.
This was done on a Dell laptop running Ubuntu 19.10, ymmv on other versions/distros.
As far as I can tell the magic string is using the uhd-soapy driver to interact with the LimeSDR: "driver=lime,soapy=0,nchan=1".
Initially I tried installing the SDR drivers and packages through the recommended PPA that MyriadRF lists on their wiki (https://wiki.myriadrf.org/Installing_Lime_Suite_on_Linux) but that didn't work. I removed the ppa, then I was able to install the necessary packages to get the uhd-soapy interface working properly. I have a few packages now showing up as installed,local and not yet sure if I want to uninstall those. I don't think they should be necessary but it's hard to tell.