simultaneous ISDN and async

[Igor Smitran]

Can i use simultaneous use to limit particular users to use just one channel 
ISDN?
And at the same time, to forbid async users multiple logins?

For ISDN users i want to limit only some users, not all.

I know that cisco questions should not be posted here and i am sorry for 
that but...
I am not sure what can i do on NAS side to prevent double channel ISDN 
logins. Cisco is AS 3620, IOS is 12.0(7)T.
If i can send some vendor specific packet to NAS that would be great.

Thank you.