Add customization to custom games
Seriously, they're called custom games, but in reality they're just ways to get all 10 people you know into a game, or sometimes play a custom gamemode such as Hide and Seek. Basically could be called Play With Friends and nobody would complain.
So add some customization. Something, anything. Allow us to put bots where they're supposed to go instead of just random places they feel like going, set how many minions come in a fleet/horde/battalion/whatever you want to call it, what order they come in, where they come(whether straight from the fountain/nexus as usual, or some random spot because why not), how often they come, let us change the stats of certain champs so we can instead have Nidalee spears heal us for a shit ton because WHY NOT? Its custom! Or, its supposed to be. Heck, make Soraka the most feared champion in the game, let us have 100% CDR so we can spam our abilities as fast as we can spam our keyboard, make our own items for stats and take passives from other items, or heck, even code it ourselves if we're smart enough.
Custom games aren't very popular right now, and what games are there are either Hide and Seek or 6+ friends playing together. Make it what its called, custom, eh?