The easiest way to securely install a managed node then is to install a standalone TMR (without any managed nodes underneath it) and convert the TMR into a managed node. Here is how to do it.
Install a TMR on the system where you want to install a managed node
Run the following command on the newly installed TMR in step 1. Make sure that the both the realtmr and this managed node system can talk, Otherwise, the whole thing fails and you may have to redo the steps all over again.
Run the following command on the real TMR. This will allocate the dispatcher number to the newly converted managed node.
Please note that in the above command, the dispatcher_id must be a unused dispatcher id in the "odadmin odlist" command.
That is it. I found this method much easier than trying to setup ssh/rexec. Hope you find it useful as well.