This is really server-dependent.
You can theoretically have a 500 error page called oogabooga.html and have the server read that instead.
Of course, it makes no logical sense, but since when did computers do that!
For the record, the following line in an Apache server's .htaccess file should do it, assuming the server admin has enabled this particular set of overrides:
ErrorDocument 500 /path/to/oogabooga.html
Graeme