Without qubicle it's basically impossible. Although I found the way how to convert kvx files to obj. That way you can extract a part of map into SLAB6, convert it into vox and then convert it into obj.
However the largest fraction of MAP I managed to extract is 94 blocks in width. That means it will take you for ever to extract and convert each one of them and assemble it in blender.
But if you are still interested or would like to render some models in blender i'll give you the link:
http://forums.3drealms.com/vb/showthread.php?t=38085RESULTS:>> MODEL <<>> MAP part <<>> COMBINED <<