For those interested, I just installed ubuntu on the expansion card, physically removing my Windows 10 ssd before doing the usb install. Everything went off without a hitch, and now if I want to boot to linux, I just f12 into the boot selection menu.
Initially I tried to navigate an Ubuntu install with the Windows ssd installed, but bitlocker caught me and I had to enter my code to get back into the OS. Lesson learned.
Anyway, I thought those interested in dual booting would like to hear about this. In short, after less than a week of ownership I’m very pleased with the framework laptop.