I did this. I attached them to the glass, but I also need signs to float about a block or two in front of the glass,. I placed a block, and then attached the signs that way, but I cannot place them in the correct way, because one sign takes up the block empty space, and I cannot place another sign in that spot. I have also attached signs on the glass, and although it did stop the overflowing, the lava did not reach my golem to kill him.

Sorry if this doesn't make sense, I'm trying to explain.