Hi,
Thanks for using our plugins.
I can try to help out here, but I am limited in helping out on customizations.
I do not have much information to provide on this.
As you figured out the additional fields field names are saved like this:
_ecp_custom_2
The filter bar does include a way to filter by those additional fields.
You could follow along with what it does, but it does not have a feature to be embedded on a non event views archive.
Unfortunately, that is about all we have on this.
Let me know if you have any follow up questions.
Thanks