Vm-builder fails when using custom mirrored repositories (release signed by unknown key)

Hi,
I'm trying to generate a lucid vm on a ubuntu 12.04 kvm host machine.

I'm using mirrored local repositories signed with a custom gpg key. When attempting to generate the vm a debootstrap error spawns:

"2012-09-03 16:24:06,690 DEBUG : E: Release signed by unknown key (key id <hidden>)
2012-09-03 16:24:06,690 INFO : Cleaning up
2012-09-03 16:24:06,690 ERROR : Process (['/usr/sbin/debootstrap', '--arch=amd64', 'lucid', '/tmp/tmprAuCmhtmpfs', 'http://<mycustomrepo>/se.archive.ubuntu.com/ubuntu']) returned 1. stdout: I: Retrieving Release
I: Retrieving Release.gpg
I: Checking Release signature
E: Release signed by unknown key (key id <hidden>)
, stderr:

some version details:

python-vm-builder 0.12.4+bzr477-0ubuntu1
ubuntu-vm-builder 0.12.4+bzr477-0ubuntu1

And this is the full command:

/usr/bin/ubuntu-vm-builder kvm lucid --debug --tmpfs - --lang=en_US --hostname=vmgeneration-test <snip> --mirror=http://<mycustomrepo>/se.archive.ubuntu.com/ubuntu --security-mirror=http://<mycustomrepo>/security.ubuntu.com/ubuntu <snip> --raw=/dev/sysvg/vmgeneration-test

Any clue on how to override this?
Thanks!