Comment 10 for bug 264727

Problem solved: See anser to the upstream bug report:

-----------------------------
he following will do what you want:

    Attribute CustomPageSize True "pop pop pop pop pop
%% Option Setting: PageSize=Custom"

In general, this works for any attribute/keyword you want to override in
the generated PPD file - ppdc/drv only provides its own version if you
don't.
-----------------------------

So the lines

  VariablePaperSize yes
  MinSize 72.00 288.00
  MaxSize 612.00 3168.00
  Attribute CustomPageSize True "pop pop pop pop pop
%% FoomaticRIPOptionSetting: PageSize=Custom"

will lead to the desired result.