> all. I can live without blob data, but not without nulls.

Nulls are not supported directly, but you can easily emulate them
by defining your own null-indicator column:

CREATE TABLE t (
a integer,
ni char(1) )

INSERT INTO t VALUES (123, ' ')
INSERT INTO t VALUES (234, ' ')
INSERT INTO t VALUES (345, 'N')

SELECT CASE ni WHEN 'N' THEN NULL ELSE a END
FROM T

CASE
===========
123
234
<null>

> Also, padding
> would increase my file sizes by a factor of 10-20 times ( Unused field space
> + a lot of 50 character nulls add up quickly). I need to be able to
> preserve bandwidth here as well. So what would normally be a 100 meg file
> blowing up into 2 gig file to transfer is unworkable.

Then just zip/rar/compress that file ...

Ivan
http://www.volny.cz/iprenosil/interbase/