I asked a similar question here and got pretty close to what I'm looking for
...but, this doesn't quite get to what I'm after, which is starting a process in a new window (not an existing window) in an existing screen session (not a new screen session).
If you are at a command prompt in a screen session, you can do this:
screen [screen options] command param1 param2
But, how do you do it if you are outside the session? For example, if you want to run this as a cronjob?