RJS and EXTjs component update (RAILS 1.2.3)

I want to use an RJS view to update EXT Panel bodies. But since the panel bodies have generated element ids, I can't see how to use 'page.replace_html'.

So instead I wrote a javascript function 'updateBody'.

In the RJS view, I want to say something like:   page.call 'updateBody', 'some_panel', :partial => 'my_partial'

I looked at the source for replace_html, and then tried:   page.call 'updateBody', 'some_panel', page.render(:partial => 'my_partial')

but that doesn't work, and neither does:   page.call ..., render_to_string(...)

Rendering the partial in the controller   @rendered_partial = render_to_string :partial => 'my_partial' does work, but it seems that there should be something easier.