Vzdump and direct backup to tape?

Question

KVM

I want to make a direct backup of the VM to tape, bypassing the intermediate backup to disk.
Such a design

vzdump 106 --mode snapshot --stdout | tar -b 4096 -cvf /dev/st0 -T -

does not work, because tar expects file headers. But I don't understand how to create and pass the correct header.
I would appreciate valuable suggestions.