How-to blacklist a package during Debian preseed ?

[Alexey Eromenko <al4321@gmail.com>]

Hi,

I have learned a trick to blacklist a package:
$ cat /etc/apt/preferences
Package: <packagename>
Pin: release *
Pin-Priority: -1

problem:
It doesn't work during d-i "preseed/early_command" stage. (due to lack of apt)
Any ideas how-to blacklist a package during Debian preseed ?

-- 
-Alexey Eromenko "Technologov"