How can I fake superscript and subscript with Core Text and an Attributed String?

I'm using an NSMutableAttribtuedString in order to build a string with formatting, which I then pass to Core Text to render into a frame. The problem is, that I need to use superscript and subscript. Unless these characters are available in the font (most fonts don't support it), then setting the property kCTSuperscriptAttributeName does nothing at all.

So I guess I'm left with the only option, which is to fake it by changing the font size and moving the base line. I can do the font size bit, but don't know the code for altering the base line. Can anyone help please?

Thanks!

EDIT: I'm thinking, considering the amount of time I have available to sort this problem, of editing a font so that it's given a subscript "2"... Either that or finding a built-in iPad font which does. Does anyone know of any serif font with a subscript "2" I can use?