A Custom PlaceHolder for Read More…

Hello everybody.
I would like to please ask for your help for a solution that I have been looking for for a long time to my problem.
I would need to have the read more function for events and locations.
The aim would be to create a read more function that appears automatically after a few characters and that allows the text to be extended by clicking on the appropriate wording “read more”, remaining on the same page and without loading a new page.
This would be useful for both good usability of the pages and SEO.
What I was thinking about would be to create a new placeholder to have the text starting from a certain number of characters onwards.
In short words:
Suppose we have a text like this:
“one two three four five six seven eight nine ten”
With the existing placeholder function #_LOCATIONEXCERPT {5, …} I could have the first five words but if I could create a further placeholder like #_LOCATIONEXCERPTOVER {6}
and create a link that would load me the words from the sixth onwards I think it would be perfect.
Any help and ideas are welcome.
Thanks in advance to everyone who will take the time to help me.