First, make sure the plugin doesn't have the option.
I'm not sure if there is a plugin to do specifically what you want, but I think you could make it work with the existing plugin. You could clone the track, then run one through the plugin that removes the vocals, then flip the other track out of phase and finally mix the two together...which should leave you with just the vocals.
So you're asking, "well, how do I do that???" Yeah, lemme think about it...