Yep, I should have known that this was a simple problem to solve... Don't ask me why, but I did not try the most obvious flicking thing on the planet: reading the perldocs for HTML::Entities and URI::Escape. Of course, I even had the answer in my post (just a little hidden):

"This is the same format that is used for query strings attached to URLs"

Now, since you are saying "but you should use URI::Escape, of course!" then you are right ;)

So a perl script to do a little work with flash:

#!c:/perl/bin/perl -w
use strict; # I am getting into the habit of using this!
use URI::Escape; # For escaping special characters

# Keys of this hash correspond to flash variable names:
my %output = (
     'infobox' => '1+1=2 & 2+2=4 yep!'
);

# Send the HTTP header (content-type does not seem to matter)
# I have used text/plain since that sounds the best ;)
print qq|Content-type: text/plain\n\n|;

# Loop through each of the variables in the %output hash
# Function - Encode characters and print them to flash
for (my ($name,$value) = each %output) {
     print qq|$name=| . uri_escape($value) . "&";
}
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How to execute this from flash (the '0' as the second argument means to load the variables in global scope):

loadVariablesNum ("path/to/script.pl", 0);