Check this out:
A company called Prestigious Society has a module that will override the navigation functions while you are driving.
This is a Toyota and Lexus specific unit.
Here is their website:
Prestigious Society - GPS Navigation Override for Lexus and Toyota
And brochure:
http://www.prestigioussociety.com/pdfpage/Toyota%20Navigation%20and%20Video%20Override%20Brochure.pdf
I am in contact with them now to find out about their unit for us 200-series owners, but it looks promising.
I will let everyone know what I find out from them.
I'm talking to them about possibly setting up a group buy option for us when the unit is available, but it should be soon.
This is great news, if all goes well!