Dear Ning,
Yes you can do that if you create a website that will be used for the replication and that will not have any content.
This website will be used to replicate the other website.
See the procedure on how to share user as explained in the video present in the tutorial step 16.
www.jms2win.com/tutorial
This procedure show the concept of sharing.
You will see how to create this "common" slave site that will be used to create the other slave site and that will share the same user. With JMS, you SHARE and NOT synchronize. This mean that the information is present only once and is not replicated.
As this "parent" slave site will be use to create the children slave site then up to you to decide of the extension that you install and which content you want to put in each slave site that you will create.
This will also help you propagate the installation of extension all the children websites.