I think that this might work...you might have to adjust it...
create a shared variable.
initialize before calling the subreport.
have the subreport update it
if the shared variable is some value (probably the initial one) suppress the detail section and/or suppress the field as desired.
basically use the shared variable as a flag.
creating a shared variable is as simple as declaring it:
shared numbervar x; //can also be stringvar, booleanvar, etc
assignment uses the 'assignment' operator :=
comparison is just =
Hope this helps, or at least points a way