You can set a systemwide default help topic under Admin Panel > Settings > Ticket, but as you initially asked for a unique link for each help topic I'm not sure if I read your post correctly recently. So just to be clear, do you want
a) the possibility to pre-select a help topic via an unique URL or
b) an unique page for each help topic, so that customers/users from different companies/departments only see their help topics, but not the help topics of others or
c) something else?
Michael