[R] Disabling shell access through system() possible?

[lists at mwoywod.de]

Hi! I'm deploying R behind a web-app on a linux-server and I don't want 
to grant the users shell access through the system() function for 
security reasons.

Is there any safe way to deny a user access to the function?

I tried
a) alter the function in the R-Sources before compiling them. Doesn't 
seem to work because system() is apparently needed during the build.
b) Redefine system() in the global Rprofile. Leads to of course to some 
warning messages at any session start and feels generally kludgy and 
unsafe.

Best Regards
M.W.