If I understand what you are asking correctly, I had the same problem. This is what I did to disable and enable the entire datepicker in Angular. I know you already have your answer but I figured I would share anyways.
Here is my HTML/bootstrap (which I got from the website you added at the top http://angular-ui.github.io/bootstrap/ almost half way down the page): All I did was add ng-disabled="disabled" to the input and button tags. disable is just a $scope variable that gets set to true or false when some event happens in my app
<div class="col-md-6, nonFields" style="margin-top:6px;">
<p class="input-group">
<input type="text" class="form-control" datepicker-popup="MM/dd/yyyy" is-open="opened1" ng-model="dtClosed" ng-required="true" close-text="Close" ng-disabled="disabled"/>
<span class="input-group-btn">
<button type="button" class="btn btn-default" ng-click="open($event, 'opened1', 'opened2', 'opened3')" ng-disabled="disabled"><i class="glyphicon glyphicon-calendar"></i></button>
</span>
</p>
</div>
In my angular js code I set $scope.disabled to true at the top
$scope.disabled = true;
Then when the user clicks a button and with the correct input I pretty much set $scope.disabled to false
$scope.shortCodeClick = function(){
$scope.disabled = false;
};
and the entire datepicker becomes enabled. With this you can obviously customize what you want to do with whatever event and flip the datepicker back and forth from enabled to disabled and back. Hope this helps.