This is pretty easy to sort out with the make your own field type instructions which can be found here:
http://www.advancedcustomfields.com/resources/creating-a-new-field-type/
I knocked together one pretty quickly as a plugin using this and CodeMirror. I only created it for use with CSS and JS code types but it’s pretty easy to implement.
Edit: I should probably point out that by quickly I mean it took less than 30 minutes.
