Practice mode

How about a practice mode, where you can practice things like farming(something like Howling Abyss with a much larger minion wave or sth) or skillshots/combo's against bots(with faster level gains and/or shorter cooldowns)? I would love to practice my farming skills on champions like Anivia, Leblanc or Swain as well as Lee Sin insecs, but whenever I start up a custom it feels like I spend too much time doing nothing and just waiting for the minions/cooldowns.

Any thoughts on this?