What is correct way to pack records

[wom@inel.gov (Warren O. Merrill)]

I want my record structures to byte align (for compatibility with
existing files).  I know about using the record representation clause
to lay them out.  I have a LOT of these to do and just wondering if
any of the pragmas would be guaranteed to byte align my fields but NOT
change the order of the fields to do it (NOTE THAT IS IMPORTANT!!!!!).

So instead of:

type MyRec is record
  Fld1 : character;
  Fld2 : character;
  Fld3 : character;
end record;

for MyRec use record
  Fld1 at 0 range 0 .. 7;
  Fld2 at 1 range 0 .. 7;
  Fld3 at 2 range 0 .. 7;
end record;

is there a pragma (or other method) that will do the same thing
GUARANTEED not to change the field order to accomplish the packing
without having to write all these record representation clauses?