We consider cost-sharing games in which resources' costs are fairly shared by their users. The total players' cost in a Nash Equilibrium profile may be significantly higher than the social optimum. We compare and analyze several methods to lead the players to a good Nash Equilibrium by temporal addition of dummy players. The dummy players create artificial load on some resources, that encourage other players to change their strategies.We show that it is NP-hard to calculate an optimal strategy for the dummy players. We then focus on symmetric singleton games for which we suggest several heuristics for the problem. We analyze their performance distinguishing between several classes of instances and several performance measures.

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