Not using ID's BSP Compiler Application to produce the BSP file! There are some open source BSP compiler projects, although somebody told me they're not fully working, but that's some time ago. Check it out:
http://map3bspc.sourceforge.net/
And then there's OpenBSP wich is not the same AFAIK:
http://www.osmanturan.com/
http://map3bspc.sourceforge.net/
And then there's OpenBSP wich is not the same AFAIK:
http://www.osmanturan.com/