This is a good idea. getmonero.org could have a page on the site where people can choose to mine for a while for a certain charity. It would be a really good marketing stunt
getmonero.org should be setup to do this.
It is an amazing idea.
We could choose also some marketing active charities and inform them about it. It would improve the XMR image.
Also donations to the development fund could be done on this way.