You can endorse the certificate(s) to yourself as trustee of the trust. But be careful if the trust is going to continue beyond your lifetime. There are special rules for S stock owned by trusts. You should consult with a local lawyer who practices in the tax area.
I hope that this is helpful.
Jeffrey L. Crown
While your S-corp may not be affected by transferring it to your revocable living trust, what happens if you pass away? That is, after all, one of the main points of a trust -- to handle your estate. If the trust is not set up properly, your corporation can lose its S-corp status when you pass away, reverting to a C-corp. If that's something you would like to avoid, I recommend consulting with a local estate planning attorney regarding your trust and business goals.
When you say that "you just set up a living trust" does that mean that you did it yourself? If so, I would suggest you go and see an attorney. The odds are that you are doing more harm than good by trying to perform estate planning on your own. On the other hand, if you did use an attorney, then you should can him/her for further assistance.
I know that you aren't likely thrilled by this answer; however, this is important stuff. The worst situation for you is believing that you have your documents set up properly and then, when something happens, others finding out that the documents that were signed were faulty.
Seriously, call an attorney.