Give away income live on capital

Came up with the following idea when researching IHT planning for a client. Basically the tax payer has ring-fenced a significant block of capital that he intends to leave to a charity. The capital is invested and produces an income that is taxable. (He pays tax at 50% on his marginal income.)

We are discussing the possibility of donating the annual income to the charity under gift aid and using capital to replace the income. In this case there are no CGT complications in reducing the capital sum each year.

Overall charity gets more and HMRC gets less!