How can I add an autocorrect mapping to the iOS dictionary?

My iPhone, running iOS 6, used to autocorrect ill -> I'll for me and I liked that. It has, very recently, stopped doing this. I suppose it makes sense given than ill is actually a word, but it is a word I rarely use and certainly use far less frequently than I'll.

Is there any way to add a correction mapping back to the iOS 6 dictionary such that typing ill autocorrects to I'll for me?

My workaround has been to add a keyboard shortcut that replaces the text ill with I'll any time I add it. Not perfect, but as a stop-gap it will do.

To add the shortcut go to Settings -> General -> Keyboard and scroll to the bottom of the page. You will see an Add New Shortcut... button. Press it.

In the Shortcut configuration page type I'll in to the Phrase entry box and ill in to the Shortcut entry box and press the Save button.

Now any time you type ill it will auto-correct to I'll.