Hey Everyone,
DISCOVERED THE ANSWER!!!!!
I recently got one of these fun little squares and I just figured out (what seems to be) a simple way to keep the clock face on. (Though, I certainly agree with the comments about the ultimate impracticality of doing so for a long time, as the the battery in this thing only has so much to give.) I'm running the latest update on it.
This seemed too easy to believe when I did it! No need to keep it empty of music! No need to keep it in Fitness running! I think this works because the clock face, stop watch, and timer are all in the same segment of it's little nano operating system.
If you turn on the stopwatch then switch back to the clock face, it will stay fully illuminated as long as the stopwatch is running. I think the limit on the stopwatch is 24 hours, but my guess is your battery is going to be dead long before that. I'd recommend setting the brightness super low if you're going to do this.
Anyway, problem solved if you want to keep it lit for however long you like. (of course you have to sacrifice the stopwatch)
Enjoy!!