How to be able to overlap font awesome icons to create a badge?

I’m creating some custom awards, and I wonder if (and how) it would be possible to overlap some icons to create one award.

For example the trophy with a star in it (fa-trophy combined with fa-star), use the fa-certificate as a background combined with fa-user, etc.

I know I could add an image instead, but I rather would be able to use font awesome for it if that was possible.