I'm trying to find my way inside the moodle code and I made something a (little) bit like what you want... it's a block which displays a random text everytime a person views a page.
it doesn't come with a GUI ! In fact the only way you can add texts to the pool at this time is by manually adding them to the file 'block_random_quote.php'
$quote = "I am not young enough to know everything.";
but that's the only thing you have to change! (And you do seem to hack a lot! )