This is a pretty cool hack or trick if you want to do this in your friends doorway. I made it in the Xbox 360.
So to make a invisible block you need
At least 1 block (of your choice
1 Grass block
Step 1: The Invisible Block
So what you do is place your block (I made a doorway to demonstrate) and then use the bonemeal on the grass block in the doorway (or next to your block) so a tall grass will appear on it then place the ladder in the tall grass. When you do this it creates a invisible block. As you can see in the second picture the faint lines of a block. and then me standing on it ( in the third picture) I hope you enjoyed this instructable and don't forget to Vote :)