Forward main number to auto attendant

[mccal18]

I have a CS 1000M (v 7.5) with 3 attendant consoles (M2250). Our main number terminates on these consoles as LDN0. I want to send our main number instead to our auto attendant (AVST Call Express 8.2), but in such a way that, if the auto attendant goes down, switchboard staff can immediately answer main number calls on their consoles. I also want the consoles to still function as the internal 0, and continue to recieve calls through a tie line from our other site.

One suggestion I've recieved is to change the Night Service to go to the auto attendant, and just put all 3 consoles on Night Mode ("busy-out").
Pro: switchboard staff can get the main number back immediately by taking one or more consoles off Night.
Con: I'd have to put additional sets (M2616s) -- into a physically crowded space -- configured as 0 for internal calls to switchboard; and I don't know how to handle the tie lines.

Any suggestions how to send the main number to auto attendant (so switchboard staff can toggle on/off) and retain all other attendant console functions?

Thanks, Chris