Thanks for the tip. I found a simple solution. I wasn't aware of the file in step #2 below until I saw it mentioned in another post.
I had MonkeyTunes working on a full MM installation, but am currently using a portable MM installation for stability reasons. MonkeyTunes was not appearing in the portable MM installation.
1. Copy the <MM>\Plugins\MonkeyTunes to the respective portable MM directory.
2. Copy <MM>\Scripts\Auto\MonkeyTunes.vbs to the respective portable MM directory.
That worked for me. MonkeyTunes was visible on the next restart of portable MM.