Case insensitive completion on ancient zsh versions?

[Kai Grossjohann <kai@xxxxxxxxxxxxxx>]

I've got a login on various systems which have zsh version 3.1 (!)
installed on them.  To add to the joy, they just have the binary, and
no documentation.

I intend to install a more recent zsh wherever I can, but in case I
can't install anything, I'd like to make my life a little better.

Is it possible to turn on case insensitive completion for that version
of zsh?  How?

Kai