% cat ~/.dataprinter
use_prototypes = 0
index = 0
align_hash = 0
hash_separator = ' => '
colored = 0
begin filter Math::GMP
    $ddp->unsee($obj); "z_$obj";
end filter

% perl -MDDP -MMath::GMP -we '
  $val = 1;
  $zval = Math::GMP->new(1);
  p [$val, $val, $zval, $zval];
'
[
    1,
    1,
    z_1,
    z_1
]
%