I don't know of a method to do explicitly what you want. Really you should be using SSH as not only do you get the encryption as a layer of security and key based logins but you also get niceties such as file transfer and more relevant in your case I suspect, remote command execution. One or both of which may solve your problem.
It would be possible to use netcat to inject commands piped in from a file to a telnet server as if they had been typed in. But you would have to manage the whole session that way (including login) which could get more than a little bit icky. I can't see an easy way of jumping between netcat and an interactive client for the same session. You could do something nasty like telnet in, put whatever you were doing in screen and get to the point where you want to inject commands. Then start a new session alongside with nc being fed a script that logs in the session, attaches the screen session with -x and issues the "typed" text. But I think at that point you need to re-evaluate what you are doing and think of a cleaner way. If not only because you are going to have to manage line breaks etc the hard way but because it would probably fail horribly as you can't manage pauses between login and shell etc.
Joking aside...I'd look into a way of doing what you want with ssh, perhaps copying a file up and then remotely executing a command with the file piped into it.