As Toolic suggested, pre-processing the file works

#!/usr/bin/perl
use strict;
use AppConfig qw(:expand);
use Data::Dump 'pp';

my $config = AppConfig->new({
  CASE => 1, GLOBAL => {EXPAND => EXPAND_ALL}
});

$config->define("VAR=s");
$config->define("AMB=s");
$config->define("DIRSKE=s");
$config->define("SCRIPT=s");

open my $fh,'<','./file.conf' or die "$!";
my $file = do{ local $/; <$fh> };
$file =~ s/[{}]//g;
close $fh;

open FH,'<',\$file;
$config->file(\*FH);         
pp $config->{'FILE'}{'STATE'}{'VARIABLE'};;
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