Shell Programming and Scripting

ok guys and gals at the moment i am perplexed (prolly cuz i been looking at it to long) but here it is.

OS: sol8
perlver: 5.8.0
shell: ksh

answer must be in perl!!

issue:
when i use pack() it packs the data at the front of the requested field space. normally it wouldnt be a problem if people followed the standard for EDI but nooooo so now this is my problem. heh

I need it to pack the data from the back.

Here is an example.

i have a number $a=12
I have to manually add ".00" onto it and pack it with spaces to fit in a 12 char field which is then assiged to a variable so i can use it later on.

so:
$a=12
$b="${a}.00"
$c="xxxxxxx12.00" (x represents a space) BUT I CANT FIGURE IT OUT.

Code:

        }
        elsif ($_ =~ /^33/ ) {
                $pad=(length($jackpot[$COUNT][2])-9);
                $aqty=pack A12, "$jackpot[$COUNT][2].00"; #THIS PACKS IT THE WRONG WAY
                substr($_,92,12)="${aqty}";
                print FILEOUT "$_\n";
        $COUNT++;

Code:

        elsif ($_ =~ /^33/ ) {
                $pad="         $jackpot[$COUNT][2].00";
                $aqty=pack A12, substr($pad,-12,12) ;
                substr($_,92,12)="${aqty}";
                print FILEOUT "$_\n";
        $COUNT++;
       }