Opportunities to set one model value based on another?

[stephenwil]

I have the scenario where I want to set one model value based on some computation of another model value.
A phone preference type ('Mobile', 'Work', 'Home') and a mobile phone number.
Both values are optional, and therefore could be blank.
If the mobile phone number is complete and valid, I want the phone preference to be set to 'mobile'.

If I want to do this on the blur of the mobile phone field - I can't. Why:
a) I can override the onBlur of the mobile phone field over Form-containers' but I'd have to replicate what form-container is doing, as it's not exposed on the interface to call it.

b) Although the form-config allows a 'global' onBlur event, it's outside the implementing class, and therefore has no access to the model etc.
I could have used 'getValue()' but that's not exposed on the interface.

c) I can override the onChange event, and then call form-containers' one, but the model on the props doesn't reflect the update of the model, validation etc that may happen when form-containers' is called. (It's one cycle behind).

There's no real opportunity to achieve the above unfortunately.