Hi @shahidt,
We come back with the great news. 
Our team has officially supported with_relationship() function that helps you to control the relationship within your metric definition.
Could you refer to our post here Role Playing Models / Model Aliases - #12 by Khai_To for more information?
So in your case, you can disable the relationship path from dim_campaigns to one of your fact model.
And then when you need to define the metric that requires that relationship, you can forge enable that one within the metric context.
If you want to try out our AQL Expressions, please let us know.
Do let me know if you have any questions or concerns.