Hi
This is possible, add ads to the every 25% or 50% text in the article without using plugin. Not manual automatic.
Regards

I not developer.
Now i using item.php to this this but this is limited Only ads introtext or fulltext.

I always using k2 elite ads (no more developing) but now, not working well with new ads from google.

Maybe in feature version K2 the option for ad slots will appear ;)

Great news :)
I am waiting to the new update and the new plugins <3