OK. You already have database containing the information used to the generate the ASCII view. You can take each ASCII representation / database definition and build an image for it. Then you rewrite to substitute the image for the ASCII in your display. As time goes on you can create new image tiles and update your database. You could even start by putting in solid color blocks.
It sounds really easy. What am I overlooking? I don't know what your back-end is written in, but overlaying a monster/character token is easy in all the languages I know.