pseudo template tags for content?

I am a plugin developer… I want users to be able to put something like

<% replace_me_with_content %>

into posts/pages, and my plugin will replace it with some other content.

Is there some way or built in mechanism to accomplish this, other than adding a filter on the_content and doing a str_replace (which seems like a high-load way to accomplish the task)?

if not – is there a filter that will run only on page content, not post content?

Thanks!