With the earlier POD, the best way is a 3rd party from the left which draws away enough support to cost Clinton several states.
Perot really only cared about NAFTA so someone like Jerry Brown leaving the democrats and going to the Reform party which opposed NAFTA could work. Perot doesn't enter and allows Brown to lead the party and pull it left on the issues he doesn't care about. Brown talked about running with Jesse Jackson as his VP in the 92 primaries which cost him NY and pretty much locked up the nomination for Clinton.
If they could keep the 7% Perot got and up it, a Brown-Jackson ticket running anti Nafta could potentially sap enough votes in the big blue states from Clinton to cost him the election.