usermod

[Steve Buehler]

I know you can use "usermod" on RedHat Linux to add a user to another group 
by typing:
usermod -G sam,frank steve
This would effectively add steve to the "frank" and "sam" group.  How do 
you remove them from those groups without editing the /etc/group file 
manually?  I can do:
usermod -G steve steve
That will remove him from "sam" and "frank" groups but would add steve to 
his own group so the /etc/group file would look like:
steve:x:590:steve
instead of just:
steve:x:590:
For the life of me, I can't figure this one out.  Does anybody know?

Thanks
Steve