That's not easy in current Q2A implementation, especially for non-developer. You'll need to modify htmlLawed component, that is used to sanitize HTML, to make it white list-compatible, or use your own HTML sanitizer (as eventally I do).
I can give you a patched code of htmlLawed, but as I said, you should be developer to be able to integrate it into q2a and reinstall it again after engine updates (not saying about code verification, but will if you really want to be sure that such changes in security critical component is safe, you should also be able to do it).
If I were you, I would better ask q2a author to make that white list.