Use of [PLOT_FORMAT,OPENMATH] in xmaxima



Hi All,
   I am using the xmaxima interface under debian testing. I was using 
the OPENMATH plot interface that results rather nice in xmaxima.
However when I installed gnuplot, automatically, xmaxima changed the 
interface to gnuplot that is not embedded and therefore is not as nice.
  How can I set the OPENMATH interface by default again in xmaxima?
 I had a look at the xmaxima tcl/tk file but I did not find any obvious 
place or even any system configuration file.
I can use the command:
set_plot_option([PLOT_FORMAT,OPENMATH]);
but I do not know where to put it.

Thank you in advance,
Antonio Amorim