What is the ruling on giving charity to the needy so that they may supplicate for me, with the certainty that Allah does not reject this supplication?

The Fatwa's Summary:

The issue of dedicating the reward of acts of obedience to living individuals is a matter of scholarly disagreement. The Hanbalis and Hanafis permit it, while the Shafi'is and most Malikis prohibit it. The supplication of a Muslim for his brother in their absence is answered; Allah either answers his supplication, or stores up the reward for him in the Hereafter, or averts some calamity from him. There are also impediments to the acceptance of supplications.