Hi Peter,
What you can do is to export your 3d files in stl ascii format, then use stl2dat to convert them to LDraw file format. You can either use it as a command line tool (http://marc.klein.free.fr/lego/stl2dat/stl2dat.html) or through a GUI, stl2dat is one of the tools included in LETGUI distribution (http://ldraw.heidemann.org/index.php?page=letgui).
Remember that dimensions of your object must be expressed in LDraw units, otherwise some scaling will be necessary (1ldu=0.4mm)
What you can do is to export your 3d files in stl ascii format, then use stl2dat to convert them to LDraw file format. You can either use it as a command line tool (http://marc.klein.free.fr/lego/stl2dat/stl2dat.html) or through a GUI, stl2dat is one of the tools included in LETGUI distribution (http://ldraw.heidemann.org/index.php?page=letgui).
Remember that dimensions of your object must be expressed in LDraw units, otherwise some scaling will be necessary (1ldu=0.4mm)