Whoever makes it would have to have invented the 2004 STS-V. The V was only made for four model years from 2006-2009. The base STS wasn't even around until 2005 my, unless you count the Touring package on the old Seville.
Moved to the STS-V forum, although I don't know that you'll find much info here.
Googling for "Northstar dry sump" reveals that ARE makes a pan - http://www.drysump.com/cadillacnorthstar.htm - but there aren't any details there. ARE is one of (if not THE) biggest player in dry sump stuff, so you might just give them a call and see if they have a "kit" for the Northstar engines.