Disable amdgpu driver without a working keyboard in UKC?

[Jag Talon]

Hello,

I recently installed OpenBSD on a MacBook Pro 15 (2017), but I'm having 
trouble getting to the actual login screen because the screen turns 
blank and turns off before Xenodm even starts.

After searching around the web for a bit, I found this thread about a 
problematic amdgpu firmware: 
https://www.reddit.com/r/openbsd/comments/k7r0bw/black_screen_after_some_boot_prompts/

I wanted to try that out by running the same `disable amdgpu` command in 
UKC, but neither the built-in keyboard nor my external keyboard work in 
UKC mode.

Is there an alternative way of disabling amdgpu when my keyboards don't 
work? Perhaps I can echo to some config file during the `boot>` prompt?

I would send a dmesg, but unfortunately I can't even log in so I 
apologize. I believe my graphics card is Radeon Pro 560 or Radeon Pro 
555 based on https://support.apple.com/kb/SP756?locale=en_US

Thanks so much!