Setting a default value for a media image field

I'm trying to set a default value on an entity reference field that accepts media of the image type. I assume I can't do this with the "Set value or default value" plugin as it seems to only work with simple text values. Therefore, I'll need to write a custom plugin.

I haven't been able to find any examples of someone else doing this, but wanted to post here to see if anyone knows of anything that could help before I dive in.

Thanks.