I also found this out a while ago, and while I can't unlock the Checkpoints for you (though I haven't done it myself since they were added!) I can tell you one thing.
Although you can't use /sethome in Dungeon Parkour anymore, you can still use /home to TP to any you made before the Checkpoints were put in - so if you you have any old /home left over from last time, you can still TP to them as before. Don't delete those homes with /delhome though - as you won't be able to set them again
I only have one there myself these days, which for me is /home finish. I put that one in when I completed Dungeon Parkour and it's at the Finish line, but it's on the side where the Bed and Signs are, so I can't really see much of Level 9 from there. I do sometimes cheer players on though. This was about a week or so before the Checkpoints were put in, so I guess there might be other players who still have /home there since we were allowed to use it back then.