All I can offer you is a commandline tool that is capable of converting some formats, including OBJ to 3DS. Includes C Sourcecode, so you may port it to Blitz, or use the binary by the commandline in a hidden mode:
http://www.melog.ch/dl/ivcon_3dconvert_win32bin.zip
http://www.melog.ch/dl/ivcon_3dconvert_win32bin.zip