[SOLVED] how to set nested parameters for an operator in my own code

Hi all,

I have the following operator in my process which contains a parameter with a list of parameters. I need to set the value of those inner parameters (i.e. the parameter with keys 'a' and 'b')  in my code. I was wondering if there is any way to do that programmatically.  --thanks

<operator activated="true" class="text:process_document_from_file" compatibility="5.3.002" expanded="true" height="76" name="Process Documents from Files" width="90" x="112" y="75">
        <list key="text_directories">
          <parameter key="a" value="C:\myFile1"/>
          <parameter key="b" value="C:\myFile2"/>
        </list>
...        
</operator>

ps. I tried to use setParameter( ) method but it accepts only Strings.