Help with simple Automator file copy script

I have a simple Automator script for updating a specified folder with files from another folder. It consists of only two actions:

1. Get Folder Contents (from the folder I drop on the Automator executable).
2. Copy Finder Items.

I left the option "replace existing files" unchecked because there's no point in replacing a bunch of files that already exist (we're talking about 4000-5000 files in the source folder).

I assumed that meant to ignore any existing files but, on the contrary, I found out that the script is copying duplicates of all the existing files -- making my target folder about 9000 files strong!

How do I get a command into the middle of this script to restrict the Copy Finder Items command to files that do not already exist in the target folder? (It would be even nicer if it could check for files that are older than the files being copied and actually do replace those as well.)

Any ideas?