but when I run a "cpan install Net::LDAP::LDIF" for example (even as administrator) it gets blocked by bit9 when running dmake

Do you mean that bit9 prevents the module from even being built (in the "dmake" phase) ? ... or do you mean that bit9 prevents the module from being installed (in the "dmake install" phase) ?

Assuming it's the latter, the first thing I would want to know is "into which directory is dmake trying to install the module ?"
Running perl -V:installsitelib would normally tell you that. Does it report a directory to which you have "write" permissions ?

UPDATE: As a double check, have a look at the INSTALLSITELIB entry in the generated Makefile. It should specify the same directory as perl -V:installsitelib

Cheers,
Rob