Which message is correct for Campaign to marketing list association in plugin

Hi ,

I have a scenario where i need to write my custom code once the marketing list to campaign association is done.It should be a post operation. I have tried using Associate message and after some research found out that it will not be triggered as Campaign entity is the OOTB entity and has its own messages like "AddItem" message. AddItem message is only supported for pre-operation . 

How can i make sure my plugin code is executed after the campaign and marketing list is associated.

Any help on this is appreciated .Thanks in advance.