Do you want to do the late addition with all brews, or just the lighter-style brews?
I would say do it as much as possible. But this doesn't need to be a very tricky process either.
Very high gravity boils cause a number of things to occur. One major thing is maillard reactions, which is actually what causes the darker colors (true caramelization occurs at much higher temps). But there are also plenty of reactions (including malliard) in a very high gravity boil that can lend to the common "extract twang".
The easiest way to do this is to calculate how much extract you need to plop into the boil for a "normal" gravity (roughly what the original gravity for the batch should be). You can use brewing software, write out equations, or use free online calculators such as the recipator @
http://hbd.org/recipator/ to figure this out.
Lets run through one with a nice standard 5 Gallon American Pale Ale batch:
For 5.5 gallons
6 lbs DME
.5 lb Victory
.5 lb Crystal 20L
----This gives us an OG of 1.052
If you dump all the extract into a 2.5 gal boil this brings your gravity in the pot to 1.114!!!
If you drop the DME in the beginning of the boil down to just 2.5 lbs, that brings the gravity in the boil down to 1.051 -- almost exactly what your OG will be in the fermenter. You've just created the same environment in the pot as you would have during a full boil.
Now this doesn't need to be perfect either. You can play around with different numbers and eyeshot the amounts going into the boil. Sorry for the long post, hope this helps clear things up!
