TinyMCE: Strip away font size

I'm using TinyMCE with wysiwyg and I have this issue where the font sizes are all over the place, depending on where the user copied the text from. Is there a way to strip away font size? I'm ok with stripping away everything if need be (would be nice to keep italics and bold though).

I realize I could fix this with css but it would be nice to get it right at the source.