import org.eclipse.cdt.core.envvar.IEnvironmentVariable;
    import org.eclipse.cdt.internal.core.envvar.EnvironmentVariableManager;
    import org.eclipse.cdt.internal.core.envvar.UserDefinedEnvironmentSupplier;
    import org.eclipse.cdt.managedbuilder.envvar.IBuildEnvironmentVariable;

    ...


      /**
       * Add a path to the beginning of the PATH environment variable.
       * This path is not persisted so its ok to perform this on every
       * startup. The existing system PATH is maintained.
       * Note:
       * 1) the PATH modification does not appear in Environment preference page 
       * (Window > Preferences > C/C++ > Build > Environment)! Rather it appears
       * in every project property >  C/C++ Build > Environment > PATH variable.
       * 2) each call to this method overwrites previous values in PATH. If multiple
       * paths are to be prepended they should be concatenated in a single call.
       * 
       * @param path The directory or directories to prepend, separated with the
       * relevant path delimiter.
       */
      public  static void prependToSystemPath(String path) {
        EnvironmentVariableManager.fUserSupplier.createOverrideVariable("PATH", path,
            IBuildEnvironmentVariable.ENVVAR_PREPEND,
            EnvironmentVariableManager.getDefault().getDefaultDelimiter());
      }	

      prependToSystemPath("c:\mypath1;c:\mypath2");

@echo off
PATH=C:\mingw64\bin;%PATH%
start eclipse.exe