Me too have experienced "specialists" who can not use regular expressions ...
Anyway, with ReDJ you can redirect everything, the problem could be that in your case the error is returned by Apache and request didn't come to Joomla/ReDJ. To be sure, I should check it, so you could send me an email at info(at)sistemistica.it.
If this is the case, the problem can be solved adding something like:
ErrorDocument 404 /
At the end of .htacess file.
Cheers,
Luigi