First get your lettering in the way that you want as a group and position it in the solid as much as possible, with just a little bit for you to see the lettering... The un-group the letters... Now make each letter negative, making sure in the attribute box you uncheck "transfer material of negative boolean" and as Matt suggests above, in the E box, make sure that the "solid when boolean rendering" is checked... Then group the letters with the positive solid and group.. And you get the effect you want... I did this lettering with elefont and it took me like 5 minutes to do the whole thing... :)