Regarding the superblock thing, I think that the easiest would be to force one block (let's say block 122000) to have the desired difficulty and then return to normal. At current rates, I expect it would take about 30 mins (expected time) to solve the world-record block. Less if we are lucky, more if we aren't. This would require everyone to update to the new client but nothing else would need to be changed.
There will be a delay on transactions, but only for less than half an hour. Think of it as "expected downtime". We could make that block have a reward of 600 to accomodate for the extra difficulty.

What do you say?