You can import the house into MED, at least you could with some of the older versions of MED.
Then remove the invisible faces between the 'blocks', and finally 'melt' the vertices of the faces which shall have no seams.

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt