Implement it yourself .
Here is how I implemented it in Perl and tested it:

Code:
# perls '%' operator implemented manually and tested
# (c) Alexandr Ciornii
use POSIX(floor);
use Test::More qw/no_plan/;
my $list=[[-3,2],[8,3],[-8,3],[-8,-3],[-17,5]];
foreach my $pair (@$list) {
  my ($a,$b)=@$pair;
  is(my_rest($a,$b), $a % $b);
}

sub my_rest {
  my ($a,$b)=@_;
  my $c=floor($a/$b)*$b;
  print "$a,$b - $c\n";
  return $a-$c;
}