thank you for your interesting suggestion!
In the version 5.4 this functionality is not available, however I have a tip for you.
Select items in physical model explorer and add them to new “temporary” workspace. Draw relationship and then either delete the temp workspace or remove the items from the temp workspace.
Step 1: Select items in Model Explorer and add them to New Workspace
Step 2: Run Autolayout to rearrange the objects on your new workspace.
Step 3: Add the relationship to your model
Step 4: Delete the newly created workspace.
If you want the relationship to appear in your main All Items Workspace, make sure the Autocomplete checkbox is enabled.
One last tip: to quickly locate existing entity on your active workspace, right click the entity name in Model Explorer and choose Find on Workspace. The entity box will be highlighted.