That perl does not have "native 64-bit support" is not entirely true. Perl has this support, but it is a compile-time option, and is usually not enabled. But when this support is enabled this task can be done with:

my $num = 10531788168169408;
my($l,$r) = ($n>>32 & 0xFfffFfff,  $n & 0xFfffFfff);
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You can tell if perl is compiled with 64-bit integer support with perl -v. It will say something like:

This is perl, vX.Y.Z built for i686-linux-64int-ld

or maybe:

This is perl, vX.Y.Z built for sun4-solaris-thread-64all

(Of course the part that's emphasized is all that's important there.)