Tims summary is a good one, thanks!
I have to add my thinking, open to scrutiny.
1- whatever needs to be done to get the a/c to an acceptable landing position above and before the field needs to be done early, to minimise ground effects. (theoretically, if this is adhered to, the problems wouldnt eventuate, as the pilot would have noticed his/her extra altitude before arriving at final and modified the curcuit to suit.)
So, slips, s turns etc, must be initiated as soon as the over-energy issue is recognised.
2-if the pilot is high-energy when arriving in the flare it is way too late, a long or harsh landing is inevitable.

concluding the above, s turns are going to be a logical option, as you are just extending your base turn, then back again toward the field and repeat at a reasonable altitude, into the wind. Unfortunately, the turns will be at a higher speed, sloppily co-ordinated with the brakes out, so if you survive them, you will probably land correctly!

The issue is one of observation, the fact is there has been previos mis-observation, so, will the pilot suddenly realise? - possibly not. The more time that is taken to realise it, the more serios the problem results.

Quite the conundrum!

thanks for a great post

bagger