#! perl -slw
use strict;
use List::Util qw[ sum ];

sub nUniqRandsSumTo {
    my( $n, $target ) = @_;
    ## Prevent infinite loop.
    die 'No solution' if ( ( $n * ($n-1) ) / 2 ) > $target;
    my @rvs;
    {
        @rvs = $target;
        while( @rvs < $n ) {
            ## pick an element at
            my $i = int rand @rvs;

            ## Can't split 0, 1, 2 into two unique values
            redo if ( my $toSplit = $rvs[ $i ] ) < 3;
            my $first = int( rand $toSplit );
            my $second = $toSplit - $first;

            ## try again if it split into two equal values
            redo if $first == $second;

            ## replace the original with the random pair
            splice @rvs, $i, 1, $first, $second;
        }
        my %seen;
        ## Do it all from scratch if we got dups
        ## Can be expensive if the target is close to the limit
        redo if grep{ ++$seen{ $_ } > 1 } @rvs;
    }
    return @rvs;
}

for( 1 .. 10 ) {
    my $target = 840 + int( rand 61 );
    my @rands = sort{ $a <=> $b } nUniqRandsSumTo( 6, $target );
    printf "sum: %3d [ %s ]\n", sum( @rands ), "@rands";
}

__END__
c:\test>834245.pl
sum: 896 [ 0 27 34 162 197 476 ]
sum: 889 [ 35 77 109 179 196 293 ]
sum: 878 [ 18 23 77 91 280 389 ]
sum: 885 [ 6 37 68 136 154 484 ]
sum: 854 [ 7 8 12 70 237 520 ]
sum: 899 [ 8 10 29 101 293 458 ]
sum: 858 [ 0 28 37 52 367 374 ]
sum: 887 [ 1 8 11 22 43 802 ]
sum: 899 [ 11 64 65 117 271 371 ]
sum: 872 [ 7 14 40 43 154 614 ]