Use Workflows to Associate Contacts w/ a Custom Object

[allieccollins]

I find Hubspot's Campaigns to be garbage compared to Salesforce's. I was hoping to use Custom Objects to create my own Campaign object. But in order to do that, I'd need to be able to create workflows where I associate Contacts with the custom object. That doesn't appear to be a Workflow Action yet. 

I would imagine adding contacts to an object via workflow would be an extremely common use-case. How else are people associating them? 

[Damotech]

I would also find associating a custom object to a deal based on one of the deal properties extremely useful. I currently can't find a way to do it through a workflow. That means I need to manually associate thousands of deals to individual Distributors (custom object)...