Rotation? Each chapter appoints a board member for a fixed term; when that term is up, the next one on the list gets a go.
There may be too many chapters for this to work practically without unreasonably short terms, though.
It's an option worth considering. If you rotate by continent (and by chapter within each continent), then everyone is at least roughly represented reasonably often. ie. You start with one of the European chapters and one of the African chapters, you then have a North American chapter and an Asian chapter, then a South American chapter and Oceanic chapter and then different European and African chapters, etc. etc.