I get your desired effect with this:

use strict;
use warnings;
use List::Util 'shuffle';
my @list = shuffle('A'..'N', 'I'..'K');
my $pick = 'J';
print sort {(($a lt $pick) == ($b lt $pick)) ? ($a cmp $b) : ($b cmp $
+a)} @list;
[download]

Technically, each of those lt's should be a ternary operation, because values for true could be different.

Update: this GR transorm also works:

use strict;
use warnings;
use List::Util 'shuffle';
my @list = shuffle('A'..'N', 'I'..'K');
my $pick = 'J';
++(my $after_pick = $pick);
print map substr($_,1), sort map {$_ lt $pick ? "$after_pick$_" : "$pi
+ck$_"} @list;
[download]