You might want to try the SetX command. I have it on my 2008 Server, though i'm not sure if its becuase I installed any addons. It was originally part of the Windows 2000 Resource Kit, but might be built in now.
NOTE: 1) SETX writes variables to the master environment in the registry.
2) On a local system, variables created or modified by this tool
will be available in future command windows but not in the
current CMD.exe command window.
3) On a remote system, variables created or modified by this tool
will be available at the next logon session.
4) The valid Registry Key data types are REG_DWORD, REG_EXPAND_SZ,
REG_SZ, REG_MULTI_SZ.
5) Supported hives: HKEY_LOCAL_MACHINE (HKLM),
HKEY_CURRENT_USER (HKCU).
6) Delimiters are case sensitive.
7) REG_DWORD values are extracted from the registry in decimal
format.
Brian