vi shell access

[Mark Bradford]

We have an application that allows the users to us vi.  What we would
like to do is to keep the users from accessing the shell.  We currently
do not allow the users to use ":!command" by setting the SHELL environment
to a script.  The problem has arisen that some of our users have learned
to use the set shell option in vi.  Is there any way of disabling this
option?  

Thanks in advance.