There's an old workaround that still works for me on the latest builds (1.4.x):
Create an executable script (I call mine "setAt4Synergy") and have it contain this text:
echo <pre>echo keycode 24 = q Q at at at at | xmodmap -
-</pre>
Run the script. You may see lots of newlines input just wait a few seconds untilit until it stops and then input '@'
Enjoy.