It's not really clear what you want if you run out of digits and the last number is less than 32. Maybe something like this will work?

use warnings;
use strict;

my $string = '79899920179';

my @nums;

while (length $string){
    no warnings qw/uninitialized/;    
    my $num;
    $num .= substr($string, 0, 1, '') while (length $string and $num <
+ 32);
    push @nums, $num;
}

print join ', ', @nums;
[download]

79, 89, 99, 201, 79