What's wrong with "tough love?"
BTW, I assume you could "cheat" and subscribe a universal userid/password (but set it to NOMAIL NOPOST) e.g.,
QUIET ADD listname [log in to unmask] universal signin
QUIET SET listname NOMAIL NOPOST NOREV FOR [log in to unmask]
create a password (you may need listserv maintainer involvement)
Then tell every subscriber the sign-on userid / password and when prompted, save it as a cookie when using the WWW interface to search