Another note: If SQL 2008 or lower, the shrink process is single-threaded = takes forever.

Despite the obvious fragmentation you're going to cause, you could try shrinking at a smaller chunk, like 1GB at a time...

There's some good power shell scripts out there to automate the entire thing:

http://www.mssqltips.com/sqlservertip/3178/incrementally-shrinking-a-large-sql-server-data-file-using-powershell/?utm_source=dailynewsletter&utm_medium=email&utm_content=headline&utm_campaign=20140605