how to set scope value using $scope.$eval() in directive?

[Eddie]

Example is http://jsfiddle.net/ADukg/182/

I get the value via $scope.$eval(iAttrs.myDirective)

The problem is setting it back with oldVal.

Looks like internally there's a setter() that can do setter(oldVal), but it is not exposed?

[ni...@bitcasa.com]

I would also like to know how to do this.  It's possible to bind the value as an accessor, but I'm not sure I'd still be able to watch it that way.