if else in a CFG file

how can I use the below in a .cfg file
% if $ (USERNAME) == "nvancaspel" || $ (USERNAME) == "bpunt"
  % if exists ($ (_ MS_CONFIG_HOORN_COF) Optimize_admin_CE.cfg)
  % include $ (_ MS_CONFIG_HOORN_COF) Optimize_admin_CE.cfg
   else 
    % if exists ($ (_ MS_CONFIG_HOORN_COF) Optimize.cfg)
  % include $ (_ MS_CONFIG_HOORN_COF) Optimize.cfg
  % endif
% endif