Most philanthropic conferences as you to first prove that you are qualified to attend (e.g. you work at or are on the board of a foundation). Here's a different approach - the Investor's Circle conference, Patient Capital for a Sustainable Future, sent me an invitation and explicitly asked that I "Spread the word. Share. Post. Forward. Print."
This seems to make sense to me and to focus the conference on the questions I think are most important for foundations, namely: "What are we trying to achieve? What resources can we apply to it? Who else should we involve?"