"set -o multiline" in ksh?

[Federico Giannici]

I recently switched my shell from tcsh to the default OpenBSD shell (ksh).
What I really miss is multiline editing of current (very long) commands 
(ksh simply horizontally "scrolls", showing only a part of the command 
line).

I know that in standard ksh this functionality is activated with "set -o 
multiline", but under OpenBSD (7.1 amd64) it gives this error:

ksh: set: multiline: bad option

So, is there any way to activate the multiline option in ksh?

Thanks