NYTimes reports that wealthy people don't give as much to charity as lower classes because they've lost ability to relate to others' needs as a result of prioritizing their own.
However there's hope and it comes in the form of a hack:
"if higher-income people were instructed to imagine themselves as lower class, they became more charitable. If they were primed by, say, watching a sympathy-eliciting video, they became more helpful to others — so much so, in fact, that the difference between their behavior and that of the low-income subjects disappeared. And fascinatingly, the inverse was true as well: when lower-income people were led to think of themselves as upper class, they actually became less altruistic."
How can this be used to close the empathy gap? It sounds like simply asking someone to project and imagine what it might feel like to be a situation different that their own produces immediate results. So make sure your campaign outreach to donors doesn't just tell a story but instead asks the target to feel what it would be like.
Overall pretty consistent with the research in Cialdini's Influence (the book you should buy and read monthly) re: self-identity and behavior.