Seems like an odd request to me, but I have my taste and you have your reason of course.
Normally the sidebar is too narrow to present a post in any readable fashion and eventually it will be pushed off the sidebar to or prolong the page to infinity.
I gather you are aware of the possibility to select how many posts to display on one page.
Go to the Dashboard/Options/Reading and change the number for “Show at most”.
If you have many recent posts, you might want to use the <!–more–> tag to just get the first lines of the post on the main page. Drawback to this is that the reader has to execute an extra click to read the whole post and then hit the back button for the rest of the posts.
Not exactly an answer to your question of course.
