Full disclosure: I don't have a Harmony to fuss with.
For units that I've controlled, there can be two commands for a button. The first would be the expected command. If the button is held, a second, usually shorter command is issued which can be considered as "repeat" or "continue". I like to think of this second command as "continue". The "continue" command will be repeatedly emitted as long as the button is held.
While it's not the same as a command with a "continue", you could experiment with sending multiple Power Toggle commands on a macro button. Unfortunately, there is only a Power Toggle command, not a true OFF command. I don't know how the TV will react to the multiple Power Toggle commands.
I found this thread that might help:
[Link: remotecentral.com].
Maybe I'll update this conversation later. I'm currently working with a 32" Frame TV on a job and I'm not liking it. There is no RS-232, network port, or audio output. I bumped into this power issue. We don't need the artwork feature, just a nice looking TV.