How can I add "free-floating" items to one layer?

I have a photo on my first layer and want to add "call outs" to it. In other words, I want to draw lines from each part of the photograph to a description of what the viewer's looking at. 

But the only way I can figure out how to do it is to add one call out to each layer, so I end up with 10 layers, one for each call out. Is there anyway to add all of these on to one layer while retaining the ability to move them around separately?