Create a 3D text layer and match the position of the text in 3D space with the wall. You'll probably have to separate the text from the wall by 1 pixel.
Another option would be to precompose your wall layer and add your text to the pre-comp. If I saw a full size screenshot with the modified properties of the wall revealed I could give you a more specific answer. Reveal modified properties by selecting the wall layer in the timeline and pressing the U key twice.