boot.cfg and autoconf

[Rocky Hotas]

Hello!
I tried to install NetBSD 8.1 in a (not so new) desktop pc and for some
reason the nouveau(4) driver creates a kernel panic.
If at boot I choose option 5 ("Drop to boot prompt"), and then type

userconf disable nouveau
userconf disable nouveaufb
boot

NetBSD 8.1 is able to perform an ordinary boot, till the login prompt. I
would like to automatically perform this configuration.
Following the EXAMPLES section in boot.cfg(5), I added the following
line to my boot.cfg:

userconf=disable nouveau nouveaufb

but it doesn't work (as if I didn't modify the file at all).
What is the correct syntax?
Thank you!

Rocky