Defining two fields as one.

I am converting some old RPG programs with internally defined files to RPGIV.

What I have run across is two fields defined as one in the old RPG program.
Ex:     1       5       lot1
        6       10      lot2
        1       10      lotall
Then lotall is used though out the program.

I know that I can do this with DS (Data Structures). Chain to file then move 
fields in the DS.  But that seams like a lot of work and extra programming.

I would like to know if there is an easier way to do this that would not 
require the use of the DS. I would prefer that whenever a chain/read is done on 
file that lotall is build and ready.

Thanks in advance for the help,
William Moore
Cal Fine Wire