dynamic :conditions for has_many?

In the setup of
class Group < ActiveRecord::Base
   has_many users :through =>user_groups
end

class User ..
...
end

for "admin" like behavior (i.e. we want to see any/all users associated
with this group), this is enough.
However, in other cases, I want something like

class Group < ActiveRecord::Base
   has_many users :through =>user_groups, :conditions =>
"user_groups.user_status_for_this_group = 'OK'"
end

what is the best way to do both simultaneously (without resorting to
something like:
user_groups.scoped_by_user_status_for_this_group('OK').collect { |ug|
ug.user} etc...

-Cole