i fear its not that trivial, what you really want is probably a raw input so you can put a string to raw bytes conversion with the desired encoding in front of it.
maybe it helps for now to do a string conversion before the node? or do you need to receive a specified encoding in the browser?
is this regarding the HTTP (Network Receiver)? what you are suggesting is that the receiver waits for the server node? this would mean you need to make some kind of link between the two nodes so the vvvv mainloop knows how and when to wait. also not that simple…
anyways, there are a few contributions dealing with the internet, maybe one of them can help: