So I just thought up something. Don't know if anyone has ever tried this or if there is even a good reason for trying it.
Brew a beer and let it ferment out. After fermentation, rack it off the yeast into the brewpot. Start another boil and throw some DME/LME/whatever you want into the pot. Depending on how much you boil off you could even do another small mash. Yes, you will boil off the ethanol and whatever else is volatile enough. Once the boil is done, throw the beer back into the fermenter. It is somewhat similar to a decotion mash. However, if some of the flavors the yeast produce stick around or are altered in a positive way by the second boil, it could be a very unique beer.
Thoughts or comments?