I cant tell from the pic very well. It looks to me that the black is the black of the shirt showing through the design. You do the same thing with what ever you are using. Be it text or whatever.
It looks like the area around the text is like cracks in concrete. If that is the case. Make a block of the same size. Fill it with a pattern fill that is similar. Convert that fill to a black and white bitmap land do a trace on it. Place that over your other block and do the front minus back.
If you dont get another answer, I will see if I can knock out a quick video in the morn, I am on the laptop right now.