IMHO, the best option is to use Surface Mode : Surface.
For this to work properly, you have to design your STL so that the text is not a solid extrusion (i.e. with a line width of 0.4mm, where each character is a closed figure), but instead a mere surface (with no width, where each character is a path).
What this implies, is that you'll probably have to draw the characters yourself, and not use typefaces.