Ok, I found the solution to the question I asked above. It is possible to get such permalinks by using plugins like
- http://wordpress.org/extend/plugins/custom-permalinks/ (I tried it and worked)
- http://wordpress.org/extend/plugins/permalink-editor/
The first plugin “custom-permalinks” allows admin to edit the slug including category. So, it is now possible to make the permalink in anyway you want.
This is what i setup in the WordPress.
First I set the permalinks to /%category%/%postname%/ So the site by default will display permalink with category name.
Suppose, If i do not want to display the category name, I can use the permalink editor to get the permalink url the way i want.
I am just posting the answer, so people can make use of it.