if we'll see into perlref.pod and search for substring {CODE} and read around a bit, then we'll calmly understand that we're able to do following trick:

use strict;

package main;

sub AUTOLOAD {
  return 'old-main-autoload';
}

package mypackage;

# let's capture that ::AUTOLOAD
my $aasub = *{$::{AUTOLOAD}}{CODE};

# now let's, as we decided earlier, have it overloaded
*::AUTOLOAD = sub {
  print "do first\n";
  #now call old one and print that returned value inside '[]'
  print '[', $aasub->(), "]\n";
  print "do last\n";
};

package main; # again

flurfish_sub();
[download]

in my case output is

do first
[old-main-autoload]
do last
[download]

But my personal advice - you're moving to C-like area or even assembler code catching area when you will really soon will complicate logic.
I think when you will see that code in your program then it is a good signal to redesign your code.
:)

Best wishes,
Vadim.