Can it be done without using a data driven radio button?
(I have some radio button options that mention legislation, which should be italic.)
That's another situation where you would need to resort to JQuery, but that has it's problems with maintainability etc.
Possibly the easiest to maintain option would be to use a selector like:
$('.id-radioButtonGroup span:contains("ONE")').html('<b>your html for the first option</b>');
So you could design your form with options ONE, TWO, THREE etc, then overwrite the html with JQUery like the above in a Page Load rule, not a Form Load rule.
In the selector above, 'radioButtonGroup' is selected because the element will have a class of 'id-radioButtonGroup', so the '.id-' prefix is required.