Calls Subpanel for Custom Module

Hi all.

If I wanted to use "calls" for a custom module, has anyone done that? I don't want to add a relationship direct as it appears on the call. I wanted to add it to the "related to" box, which you can do by adding it to dropdown called parent_type_display but this doesn't add the calls subpanel to the custom module, has anyone managed this without code?

If I add direct to a relationship it splits it out, so I want to use that standard related to box but also have the calls subpanel on the custom module.