Since the object is independent, the best way is to use the API "Schedule Campaign" (Schedule Campaign » Marketo Developers ) or "Request Campaign" (Request Campaign » Marketo Developers ) Calls. You will be able to set tokens values in the API call and use these tokens values in the content of your email.
If you do not want to develop too much and you can have a RSS feed of your object, you may want to consider the Digesto solution from Perkuto (Convert RSS Feed into Marketo Emails with Digesto, a Perkuto product. ) That can exactly do this : create the text of an email in Marketo from a RSS Feed and send it to a list of subscribers.
I know the Perkuto guys and that definitely can be an option for the trigger. Any ideas on potential batch without manually having to grab the content and update the template? I suppose it's difficult because its a one to many relationship, but maybe with email scripting?
There's no built-in functionality to grab content from a custom object which does not have an association to lead records. This would require custom development, and probably using Schedule Campaign and token replacement. The alternative would be to add an intermediate association object, in which case you could use email scripting to grab the content from the object.