figured it out for anyone who is having problems...
* find the executable itself - probably in /(your hard drive)/Applications/The Sims 3.
* Right click on it, and select "show package contents".
* Open the "contents" directory if it isn't already.
* You will see a file named info.plist. Open that by dragging it onto textedit. Don't move it out of that directory! You might want to take a backup first.
* Scroll down to the line after this one:
<key>CedegaGameName</key>
* Change the last part to read TS3.exe instead of S3Launcher.exe. Be careful not to disturb any of the rest of the file or mess with line endings. It's XML and an extra return shouldn't matter ... but you never know.
* Save and quit textedit.