There are a couple of ways I can think of. You can use DrawingDoc.InsertModelDimensions, which is the insert model items, but it has a few options in the API. You could possibly enumerate over all features in your part and then call InsertModelDimensions(2) which adds all dimensions of the currently selected feature.
Another way is to add the dimensions programatically with AddDimension2, but that would involve selecting the entities to dimension (which is a bit of work). The API documentation has an example of this in the VB examples. Coupling that with traversing the features you could possibly get what you want.
Jonathan Anderson