Is there a politically correct version of the idiom that will not offend bird-lovers? I am not aware of one, but that should not stop us. We can surely think of one. The Chinese say 一箭双雕。

The old proverb "to kill two birds with one stone" means to achieve two objectives with a single effort. I agree that It would be amazing if someone slinging a stone at a bird got one bird, let alone two. Ovid had a similar expression in Latin nearly 2000 years ago. Related phrases were in English and French literature by the 16th century. Thomas Hobbes used the modern version in a work on liberty in 1656: 'T. H. thinks to kill two birds with one stone, and satisfy two arguments with one answer.' Source:"Dictionary of Cliches" by James Rogers (Wings Books, Originally New York: Facts on File Publications, 1985). http://www.phrases.org.uk/bulletin_board

You could send a charitable donation in the company’s name. This way, we show our appreciation for their business, and they get recognition for the contribution to a worthy cause, without seeming like we’re trying to influence their decision. it is really a "two bird one stone".