Issue with creating a new message when 2 messaging widgets on the same page

I have an application with 2 message objects. I have a user role that requires to see the messages in both message objects and it is best if they can see both sets of messages on the same page so that all messages are in one place.

I am able to display the 2 message widgets fine. The issue is if I want the user to be able to create new messages. This is because the Messaging widgets will only allow me to pick from messages related to the base object of the page. One of the Messaging objects is on the base object, so I can get a list of messages for the user to select from OK. However, the other Messaging object hangs off a data object that has a many to one relationship with the base object of the page. There are therefore no messages for the user to select from.

Does anyone know of a way to get the list of messages for ‘New Message’ to be obtained from a data object relating to the base object of the Messaging widget rather than from the base object of the page?