You could explicitly make superscript and subscript font sizes equal to the base size, or just apply super and sub alignment without changing font size
Code:
sub, sup { font-size: 100% }
or
Code:
span.moveup { vertical-align: sup }
span.movedown { vertical-align: sub }
(I'd prefer the second, because the texts are not really superscripts and subscripts.)
It could work, but you don't have control on the exact vertical spacing.