So, I finally found a way to make locking dungeon doors using re-skinned bonemeal and saplings. Majority of commands are in functions and a bit of other stuff is laid out in-game poorly because I'm lazy. It includes some rooms of a test-dungeon to play around in. It also has some trigger events done with testfor (summoning mobs).
Feel free to use this system in your own maps. I'd like credit, but its not necessary.
Here's the download (mediafire):