I'm not sure if such a thing is possible with LibertyBSD. I doubt you'd be
able to do a kernel-less installation, but I'm guessing that you might be
able to do an installation into a new partition from another operating
system. The OpenBSD base system does not contain packages; if you want to
remove or add a component for a custom installation, you're going to have to
modify the source
You might want to look at these pages for something to get started with:
http://undeadly.org/cgi?action=article&sid=20140225072408
https://github.com/jedisct1/yaifo/blob/master/README
Unfortunately, I haven't done any of this before, so I can't be of much
assistance. If you get it working, post back so that everyone else can see
how you did it.
Good luck!