I am still but an egg myself, but here was what I came up with (including my testing code). Did you want a comma after the last character, as in your posting, or was that a typo?

#!/usr/bin/perl -- -w
use strict;
use diagnostics;

my @test = ( '"this is a test"', '"anStr"' );
foreach my $item (@test) {
    print($item, "\n", &jc($item), "\n");
}

sub jc {
    my ($line) = shift;
    my (@parts, $i);

    @parts = split('', $line);
    $parts[0] = '{';
    for ($i = 1; $i < $#parts - 1; $i++) {
        $parts[$i] =~ s/(.)/(byte)'$1',/;
    }
    $parts[$#parts - 1] =~ s/(.)/(byte)'$1'/;
    $parts[$#parts] = '}';

    return(join('', @parts));
}
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UPDATE: In the spirit of "there's more than one way to do it", a (hopefully) cleaner version of the jc() routine than above.

sub jc {
    my ($line) = shift;
    my (@parts, $i);

    @parts= split('', $line);
    (undef) = shift(@parts);
    (undef) = pop(@parts);
    for ($i = 0; $i <= $#parts; $i++) {
        $parts[$i] =~ s/(.)/(byte)'$1'/;
    }

    return('{' . join(',', @parts) . '}');
}
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I considered using a two-pass loop performing a pop() then reverse() on the array to remove the quotes on either end, but I think that would have been more work on the computer.