Create file ~/.MacOSX/environment.plist and edit it with Property List Editor or some text editor. This will affect Finder and all other GUI apps launched from the dock.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" 
                       "http://www.apple.com/TDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>PATH</key>
        <string>/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin</string>
</dict>
</plist>