You can use the tree filter to hide attachments in the tree:
Loading Image
This way when you select an image in the viewport, the slot is selected in the tree. Does that help?
Edit: Ahh, I see. You are in animate mode and clicking a region, and you want the slot to be selected. Is that right?
I wonder, should clicking a region in animate mode select the slot? Or maybe the region attachment, like in setup mode? Regions don't have animate mode editable properties, but maybe you want to see the region selected in the tree, to pick another region. If you want the slot selected, the tree filter can be used. I worry it could be annoying, but then image selection can be disabled if it is unwanted.
Task added:
https://waffle.io/EsotericSoftware/spine/cards/58ac427674a560d70017810a