Measuring with transparencies

I often need to measure a distance between features of different parts in an assembly where the only way I can see what I need is by making one or more parts transparent. But once I do, the features I need to select are no longer selectable. For example, I would like to know the distance between these two holes

 

 

I am able to select the hole in one part but not the one in the part which has become transparent.  What is the best solution for this ?