Importing undelimited files (Flat Files or Fixed-Length records)

I've got to load some large fixed-legnth ASCII records into PG and I was
wondering how this is done. The Copy command looks like it works only
with delimited files, and I would hate to have to convert these files to
INSERT-type SQL to run them through psql.. Is there a way one can
specify a table structure with raw field widths and then just pass it a
flat file?