Adding multiple names with a pipe didn't work.
Topic on API talk:Watchlist feed
Is it possible to add multiple wlexcludeuser variables?
No, it's not possible. Internally, the condition that's used is "rc_user_text != <wlexcludeuser>", so only a single user is possible.
But maybe we can change internal code to sth like:
preg_match( '/(^|\|)' . rc_user_text . '(\||$)/' , <wlexcludeuser> ) == 0