Using aer.bst, three authors appear in the text with all three names listed (as opposed to "et al.")

I'm using natbib with LaTex: \usepackage{natbib,har2nat}

For aer.bst, citations with 3 or more authors are listed using et al. I need to modify the bibliography so that citations with 4 or more authors are listed using et al., but that citations with 3 authors have all the names written out. For example, I want "See Adams, Brown, and Clark (2003)" as opposed to "See Adams et al. (2003)."

Is there a way to do this?