Retailers face the problem of meeting instantaneous and variable loads using two strategies: i) purchasing electricity from the pool market, and ii) signing bilateral contracts with producers. Since pool prices are highly volatile, retailers sign bilateral contracts with generators reducing the exposure to pool prices risks. Ideally, retailers would like to match sold energy to customers with energy from bilateral contracts. However, unpredictable variations in customers' loads force retailers to buy or sell energy in the pool market. This paper analyzes and proposes, from the retailers perspective, a model to set price changes which encourage customers to shift their loads considering time-of-use tariffs. This load redistribution will produce savings for the retailers, reducing the energy bought in the pool market during periods with high prices. On the other hand, customers redistributing their loads will get savings according to the new prices. Uncertainty on pool prices and customer elasticities are accounted for via stochastic programming. Risk is properly quantified using the conditional value-at-risk measure. A case study is solved to illustrate the efficient performance of the proposed methodology.