Stored Procedures, Security, Xp_cmdshell

To try to secure an outside web application we set up a user that
only has permission to execute a series of stored procedures that are
related to the appliation. Unfortunately a couple of those stored
procedures have to access system resources outside SQL Server so we
are using a call to xp_cmdshell from inside the stored procedure

SQL Server apparently won't let us do that unless we give our
restricted user (who is calling the initial stored procedure) execute
permission on xp_cmdshell. This, of course, negates most of the benefit
of setting up a restricted user. Is there some simple way I am missing
of running xp_cmdshell from inside s stored procedure without the user
calling the stored procedure having execute permission on xp_cmdshell?