OK, if it is Sigma SA mount, it has the same flange to focal plane distance as EOS cameras (44mm).
Theoretically, it should be possible to remove the Sigma flange and install one of those cheap M42->EOS adapters (from ebay).
However, I would still need to investigate some more, or to see the actual lens to let you know if is possible and what would it take to do it :-)
More about it here on Wikipedia:
http://en.wikipedia.org/wiki/index.html?curid=6773242