What platform are you on? FreeBSD will let you set the entire command line (although it will suffix it with (perl-5.8.8) or whatever).

Be that as it may, if you are sufficiently paranoid to want to do this, remember that there will always be a race condition between the moment the kernel launches your program and the point in time at which you'll be able to set $0 to something else. Someone may manage to obtain the information you so desperately want to hide.

Much better to adopt one of the approaches outlined by apl, and not have to worry about hiding it at all.