[support] Randomly display one block from a list of blocks

[George]

hi, ok, so i'd like to display one block from a set list of blocks 
randomly in one particular region - like, latest news, latest articles, 
advert etc (each with different designs). for anon views, i wouldn't 
really mind if it only updates when the cache expires.

after looking through the module list, i didn't seem to find anything 
suitable, so i've considered writing my own module - like a block 
switcher module where modules for one region are randomly switched, but 
before i do, is there already something that could actually do this out 
there, just not well known?

thanks