Nesting a custom interface extensions in a custom interface page

I want to make a custom interface dashboard page that has a more flexible grid layout, but I want to  develop all the interface elements that could populate that layout as individual custom interface elements. 

E.g. I click a ‘+’ icon in a block of my custom dashboard interface and click Custom option to open the  ‘Add Custom Element’ dialog box. From there I can add a custom interface element to that block.

Is this possible today or do I have to develop all the dashboard options with within the dashboard page element?

Thanks!