Sorry, I just happened across the LVM2 Slackware package earlier today. I haven't tried it myself.
I see what you are asking now. I have a second Slackware box I use to "test" packages on. Maybe I could try it out and maybe post some info on "what not to do". There isn't anything important on it, so it wouldn't be any great loss.
Until then, maybe someone else could help you with their experience.