How to create Engineering Workflow Management work item dependencies using drag-and-drop between plans

I have two Agile teams, Web and Mobile, which have dependencies between their work items.

I would like to use drag-and-drop techniques to create dependencies between these work items.

To facilitate this, I have created a custom view, Work Breakdown with Dependencies, to the Product Backlog plan type that is found in the Essential SAFe 4.5 process template.  This view adds Blocks and Depends On columns to the plan type's base Work Breakdown view.

I've created a Product Backlog plan for each team, with each plan's Planned For iteration being the same -- PI 4.  I've organized the work items in each plan by Iteration, thus work items in each plan are shown for Iterations 1 - 5 of PI 4.

I have attempted to use drag-and-drop to establish a Depends On link between a work item in one plan and a work item in the other plan.  I have attempted to do this by grabbing a work item in one plan and dragging it to the Blocks cell of the target work item in the other plan.  I am not able to complete this operation -- I get the "circle with diagonal strike-through" icon that indicates this is an operation that is not supported (or permitted).

Are any of you aware of something which can be configured to enable such a drag-and-drop operation to be supported across plans?  Or, do we simply not support this type of operation across plans?  I know that this is supported using a single plan.

Engineering Workflow Management 6.0.6.1.