Diplomat

This does not require multiplayer - but does require that you are in a team with another empire (AI or otherwise) or have allied with them via the diplomacy options.

In the latter, neither a Home Planet Victory nor an Eradication Victory is not possible (as you would need to destroy your ally to win) - but a Colonization Victory (occupy >51% of the map) is winnable! Just make sure your ally doesn't get there first... Colonization Victories must be enabled in the match settings when you start the game - so be sure to check this.