Expandable post summaries are great to use for those long entries and the HTML code you place in the template works for each and every post you publish. This is a great hack for expandable post summaries by Ramani over at HACKOSPHERE. It works very well, thank you! Go to HACKOSPHERE and follow these steps he has outlined for you to do the expandable post summary for each post.
Open a new window and go to the Dashboard, click on Layout for your blog, click on Edit HTML and you will see Edit Template. Go to the top right and you will need to check the 'Expand Widget Template'. You need to do this otherwise you won't be able to find the area of the template to copy and paste the code that Ramani is referring to.
Selective Post Summaries can be implemented by omitting Step 3 in Ramani's instructions and adding this HTML code from Step 3 to the individual posts that you want to make an expandable post summary. This solves the problem of each and every post having a 'read more' at the end when there isn't anything more to read.
The image below will show the HTML code in red that should be added to your post when you want to make a selective post summary. Edit each post using this HTML code and it will automatically show the 'Read more' at the end of that published post.
Click on image to enlarge