I assume you're talking about dialing in with SPM. Assign a line to remote access, either dedicated, or shared during night service. Make a barrier code, and then assign that barrier code to system programming. Call in on the remote access line, after 2 rings you get a stutter dial tone, enter the barrier code, you get dial tone again, enter *10 and you're transferred to the internal modem.
If you have DIDs, renumber the remote access code from 889 to an available DID instead of using a CO line as remote access. Still use the barrier code.