I used to make pictue frames with modeling paste and pipe them like you would on a cake. So since I started working on cakes I fugure this might work on them also. I cut a piece of plexi glass the size I need and print my design or lettering on the computer. I trace the design on the back of the paper and tape it to the underside of the glass. Be sure to look on the other side to make sure when you pipe it on the glass it will be in reverse. This will make it print on the cake right. I then choose the tip I want to use and pipe the modeling paste on the plexiglass and let it dry. I have also used modeling paste light it is a little more pliable. After it dries I put a piece of plastic wrap lightly over the top of the cake and lightly lay the plexiglass on the wrap and inprint. Then you can pipe the design or lettering on the cake.
I forgot to tell you not to use the imprint directly on the fondant or icing. Be sure to use the plastic wrap.