In concept and theory it is possible to exclude the manual receipt step in Com_B

In company A set the delivery route (believe this is already done)

Pull from Com_A/stock 

Destination Inter-company transit tOperation- delivery order (Com_A)

To have this route trigger from sale order of Com_A, set the customer location as inter-company transit. 

Maybe create a new location with type transit specifically for this process.

In Com_B create a route

Push from inter-company transit

To Com_B/stock 

Operation - receipt (Com_B)Manual step option

The practicality and limitations would need to be tested.

1. Return operations from receipt wouldn’t be possible as the push rule would end up creating another receipt operation back from inter-company to Com_B stock.
An alternative return route is defined

2. not sure if the Delivery order and SO in Com_A would be updated for returns

3. With multiple customer deliveries to inter-company transit not sure if the push route creates and propagates to a single receipt operation or multiple operations with receipt operation having customer (receive from) populated

This is critical as Com_B would need to assign ownership to the products received to be treated as consignee stock

4. Consumption/ delivery out of Com_B. Guess this process remains unchanged as it is currently.. manual delivery order or if sold, a PO for customer 

5. Reporting - Com_A might not be able to report on products in customer location as these products get moved to another location.

Not sure if this helps with some ideas and thoughts!

Sorry I did not find any solution to this, and finally gave up.
I also did not try with latest Odoo versions, it could have evolved since then.
I'm still interested if anyone has a solution / workaround for this case!