The Make Delphi action looks only under HKEY_LOCAL_MACHINE, not HKEY_CURRENT_USER.
Another option would be to check 'Do not run rsvars.bat before MSBuild' on the Options tab and specify the appropriate rsvars.bat command in the 'Command to run before main command' field on the Advanced tab.
http://www.kinook.com/VisBuildPro/Ma...optionstab.htm
http://www.kinook.com/VisBuildPro/Ma...dvancedtab.htm