iOS Long Press Button

I am putting together a simple single-player puzzle type app that has undo/redo capability. I would like to provide the ability to undo/redo a single action via a button click OR to undo/redo multiple actions via a picker view.

From a design point of view, is it better to use four buttons (undo 1, redo 1, undo via picker, redo via picker) or to use two buttons (undo/redo) where a tap indicates a single action and a long press brings up the picker view.

On one hand, the two button approach provides a tighter appearance. But, I'm concerned that the long press action is not an obvious thing to do.

I've tried reading through Apple's Human Interface Guidelines, but it seems to be silent on this.

Thoughts?