Quick & dirty "docs" on how this was done:

jebba: crispy1: see the source here: http://devel.lulzbot.com/AO-100/hardware/dual/biz_card_code/ In particular the difference() in here: http://devel.lulzbot.com/AO-100/hardware/dual/biz_card_code/biz_triple_lulz.scad
crispy1: jebba: so it looks like you build the STLS to properly overlap when brought into slic3r's plater at the same coordinates?
jebba: crispy1: kind of like this:
jebba: 1) grabbed biz cardholder off thingiverse. Any of them will do
jebba: 2) convert our font to openscad
jebba: 2) convert font with OpenSCAD-Font-Importer ....
jebba: 3) do mini file that has the STL in openscad
jebba: Like this line:
jebba: color("green") import("PlainBusinessCardHolder.stl", convexity=5);
jebba: Then you render that.
jebba: Then bring in the text and move it around changing the values at the top until you have it how you want.
jebba: So you can F5 and see the biz card + the text exactly how you want the final piece.
jebba: Then uncomment the difference() line and render/compile it.
jebba: This took forever with openscad current, so i grabbed the latest git and it was reasonbly fast.
jebba: Then export the STL, which will be the card holder with holes in it where the text is.
crispy1: jebba: sounds like quite a quiteflow
crispy1: *workflow
jebba: Then comment out the bizcard holder itself
jebba: and render just the floating text
jebba: then export the floating text as an STL
jebba: then go into slic3r and do: Combine multi-material STL files
jebba: do the biz card first, then the text.stl
jebba: then export that as an AMF.
jebba: Then load the AMF into slic3r itself, and export the gcode.
jebba: Then print with pronterface.
jebba: crispy1: and you're done!