I find it kind of hard to read. The /e alternative I mentioned would be something like:

$stream =~ s/(.)/$1 x 4/eg;          # Without extra space
$stream =~ s/(.)/($1 x 4).' '/eg;    # With extra space
[download]

I didn't include the first one on my post because it felt it would be too many advanced features for a beginner (s/// operator, regex, capture, eval, /g modifier, x operator). But now that I've actually written it down, I find it better than $1$1$1$1: it's actually more intuitive when you read it, and looks less like line noise.