... turns out to be pretty simple. Take some screenshots and either reduce the height to 512 or leave it at 768 and figure that the bottom third will be covered. Then put them in the raw/en/logo subdirectory of your LOTRO folder (the one in your Program Files/Turbine folder, not the one in My Documents). Name them:
lotro_generic_teleport_screen_01 through lotro_generic_teleport_screen_10.
I have three or four in there now and it's a nice surprise when one pops up during loading.
I hate ads. ... and the character models are SO ugly.