This script + php WordPress interface shows the latest post's url in your psm.
When it udates your PSM it only replaces the url, so you can other things without them being overwritten.
Licensed under the GNU GPL v3
Note that the setup is moderately hard and not reccomended unless you know how to edit config variables in the script, and have good knowledge of your webhosting.
Make sure you read README.txt before you do anything.
http://files.1337z.com/dev/WordPress-PSM Latest Post Interface.zip
Happy blogging.
PS. Yes, the javascript code is quite messy.
* Baggins huggles PHP and SQL