You can do this by editing the xml for the radio button. Click on the radio button and then click on the XML Source tab, you'll be placed in the source at the code for the radio button.
Between the <field></field> tags, about halfway down there should be a line that says <para vAlign="middle"/> (not the one inside the <caption><caption/> tags). Change "middle" to "top".
Once you've got it the way you want it you can save that button to your object library for re-use.
