OK, looking at this through Firebug…
The Dialog control create a div with a class called ui-dialog-buttonpane, so you can search for that.
If you are dealing with multiple buttons, you will probably want :first and :last attributes.
So, $(".ui-dialog-buttonpane button:first) should get you the first button.
and $(".ui-dialog-buttonpane button:last) should get you the last button.
From there you can modify the css/style to put each button on the right and left (modify the float values).
Anyway, that is how I would approach it right now.