You could wrap your routine in no warnings 'redefine' (which is lexically scoped):

...
{ no warnings 'redefine';
sub redirect
{
    # code for redirect will go here
}
}

# CGI's redirect() can then still be used fully qualified:
# print CGI::redirect('http://somewhere.else/');
[download]

Alternatively, don't import ":standard" functions from CGI module (which is what imports a redirect function (among many others) into your namespace), and use its OO interface instead.