That is a interesting question.
I think you can solve it, if you use a shader that projects a bitmap on a surface.
In this bitmap you can save the input-text. The saving of the text into the image could you do on pressing a key.
A texttur-projection-shader you could find in the game-studio wiki:
http://www.coniserver.net/wiki/index.php/Texture_projectorI hope i could help you a bit.
