I have not seen others but here are two attempts. Anyway i bet on tybalt89's regex ;)

Discipulus => sub{
    my @list = @input;
    my @neg = sort {$a<=>$b} grep { $_ < 0 } @list;
    my @pos = sort {$a<=>$b} grep { $_ >= 0} @list;
    @list = (@pos,@neg);
    Compare(\@list,\@output) or die "@list" if DO_CHECK;
},
Discipulus2 => sub{
    my @list = sort {$a<=>$b} @input;
    push @list, shift @list until $list[0] >= 0;
    Compare(\@list,\@output) or die "@list" if DO_CHECK;
},
[download]

UPDATE what I first imagined was a sort block.. now after the right dose of spaghetti..

Discipulus3 => sub{
    my @list = sort {    
                     (( $a >= 0 and $b >= 0) 
                        or 
                     ($a < 0 and $b < 0  ))     ? 
                     $a<=>$b                    : 
                     $b<=>$a 
    } @input;
    Compare(\@list,\@output) or die "@list" if DO_CHECK;
},

#OUTPUT
               Rate  Discipulus Discipulus3 Discipulus2
Discipulus  46252/s          --        -14%        -46%
Discipulus3 53805/s         16%          --        -38%
Discipulus2 86380/s         87%         61%          --
[download]

L*