Install mongos as a service with the default service name
To remove run mongos.exe --remove. This should allow the service to be removed without validating a configdb is required. This fails with no args for --configdb
c:\mongo\mongodb-win32-x86_64-2008plus-2012-07-09\bin>mongos.exe --remove
Tue Jul 10 13:07:33 error: no args for --configdb