Bulk Plan: how to consolidate a delivery + return pair on a single shipment?

We have two order releases on the same lane in opposite directions: a delivery (A → B) and a return (B → A). Our goal is for the Bulk Plan to build one round-trip multistop shipment (A → B → A). Instead, it builds two separate direct shipments, because the cost saving check of the multistop merge fails. The root cause seems to be that the two available rate records are tied to different equipment groups, and the combined shipment is evaluated with only one of them.

We do not want to solve this with Ship With Group. This is a single test case, but the real requirement is to have this behavior working for a large volume of orders released to the automatic planning (Bulk Plan), with planners only reviewing the result when needed. Per-order manual setup is not an option for us.