I don't think this is possible by default. You should need to program this yourself by limiting the time when transmitting chunks (by adding delay).
The more important question is: why do you want to do this??
Even when limiting the speed, it might still be a problem if you have too many users (because speed of the transfer isn't the only thing the server does). In that case you might be better off installing a nginx instance in front of your TFPHTTPServer to limit speed and connections.