I was just shown “the” solution by Jason Foreman (@threeve). On your view controller (yes, view controller) add inputAccessoryView: and return the view you want to dock at the bottom and move with the keyboard. It just works. The view doesn’t actually need to be in your view hierarchy it will be inserted by the view controller automatically.
edit: also implement canBecomeFirstResponder and return YES (as noted by Max Seelemann). reloadInputViews can be handy too.