[Bug-tar] Adding non-materialized files from a stream

[Ryan Jud Hughes]

Hi.  I have a feature request.

I have a bunch of data being created on the i/o stream.  I want to add 
this data into an existing, materialized tar archive as a file.

Traditionally, I would do something like this:
% create_data > big_file.dat
% tar -rf existing_tar_archive.tar big_file.dat
% rm big_file.dat

Of course, the big_file.dat that I'm creating can be big.  I'd rather not 
use the above approach because there will exist a time where I'm storing 
that data on my disk twice -- once to materialize the data, and once as 
part of the tar archive.

I would rather be able to add it directly to the tar archive from the 
stream:

% create_data | tar -rf existing_tar_archive.tar -

Of course, I would need to be able to name the file somehow.  Pehaps an 
argument for that.

% create_data | \
    tar -r --stdin-file-name=big_file.dat -f existing_tar_archive.tar -

Did I miss something in the docs?  Is this actually possible to do and I 
just missed it?

If not, would this be a friendly addition to tar?  Is this as easy as I 
think, or are there technological limitations making this difficult?

Okay, thanks.

--Ryan