sub test {
    my $result = $object->createNewObject() || return;
    push @results, $result;
    return $result;
}
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sub test {
    push @results, $object->createNewObject() || return;
    return $results[-1];
}
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One note:

The original code had return undef, your code has just return. They are not the same.

A bare return is basically equivalen to:

return wantarray ? () : undef;
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your solution is equivalent to:

return wantarray ? (undef) : undef;
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i.e. returns an array with a single element with an undefined value. As opposed to an empty array.

Liz

Good observation, and it's good you bring it up. The point is that a list with one element evaluates as true. Most people who say return undef or return 0 actually just want to return a false value, not an explicit undef or 0. It's good habit to use an unadorned return to signal falsehood; something as innocent as

if( my ($obj) = test() ) {
    # ...
}
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can trip you up.

Makeshifts last the longest.

You could do

sub test {
    return 
      ($results[ @results ] = $object->createNewObject() ) 
      || pop @results;
}
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which I think is syntactically equivalent to your original. Whether you would want to is another matter :)