There's no good way to do that.
Due to privacy concerns, the mods generally cannot check alts for you, and my current method (lengthy investigation: comparing memes, speech patterns and activity) is imprecise. Despite substantial efforts to curb alt voting, several probable alts still snuck through in the last election. There isn't an easy answer to this.
Plus: people could easily use multiple accounts with VPNs that wouldn't immediately be apparent, even to mods.