How to retain a place holder for missing data

Here is my problem.

We receive a data.txt  file from one of our new clients via email, which 
contains a pc file of names, addresses, city, zip, current balances, etc.
We require them to send the file in fixed format, fixed length file, as 
the only requirement for a file we will receive.

It looks like they initially created the file using as400 query, based on 
a file layout they sent me.

My problem is if any of the data is left out, or zero, the data all slides 
to the left, and destroys the fixed format of the file.

How can I correct this problem of a missing place holder.  I know there 
must be a normal way of sending or receiving this file, (not excel) to 
solve the problem.

 Hope this is clear.

Appreciate any help.

Darrell Lee
Information Technology
Extension 7127