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]
Caution: Contents may have been coded under pressure.

In reply to Re: Optimizing a sort function (wrap-around alpha) by Roy Johnson
in thread Optimizing a sort function (wrap-around alpha) by SineSwiper

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