Running a command on Windows only if the exe exists

[jmp242]

exec { 'Lenovo System Update':
          command  => '"C:\Program Files (x86)\Lenovo\System Update\tvsu.exe" /CM',
          onlyif   => 'if exist "C:\Program Files (x86)\Lenovo\System Update\tvsu.exe" exit 0 else exit 1',
          timeout  => 10800,
        }

The problem is apparently that onlyif is failing to exit 1 (i.e. not try and run the command) when the exe doesn't exist. This is testing on Windows 7.

My googling implies the above should work - so before I try something totally different, is it the puppet wrapper that's having an issue? How does everyone else handle spaces in filenames likr this?