How to disable TouchScreenKeyboard for InputField?

I have a multiline InputField and have had nothing but grief with getting the size of the TouchScreenKeyboard on iOS 9.1. I wait until both active and visible, but the area rect is still zero. I hear that Android has similar woes.

I resolved to create my own keyboard and gain more control over when it shows up and goes away.

The problem is I can't figure out how to stop the TouchScreenKeyboard from showing up when the user selects the InputField. There's no choice for Keyboard = none in the InputField's inspector for instance.

if the TouchScreenKeyboard can only be disabled globally, that's fine too.

Using Unity 5.2.2