Q.

A.

The key is good community development.  Utilise your existing networks and links.  Tap into existing groups and speak to people who work with the hard to engage groups to find out the best way of communicating with them.

If after this you are still concerned then consider adding limiters on funding or themes - for example a minimum amount to be spent in each area or on each theme or a maximum amount that can be spent on each area or theme.  That way you will ensure that each area or theme will at least get a minimum amount of spend and others don't get more than a certain amount of spend.

Monitoring representation of participants is a good way of ensuring ongoing good representation.  If you have under representation at one event you know to target that group for the next event.