Moogle shares results of his exploratory hacking with the ASICMiner Block Erupter, using an external clock signal and variable voltage -
I used a 10K ohm pot to adjust the core voltage with a volt meter on the pin I soldered to the main asic core voltage line. You should be very careful if you use my method and always have a volt meter on the asic core voltage line. I mostly did changes with the Block Erupter connected to my bench power supply with the current limited to prevent any mishaps.
Sadly, one ASIC was lost during the procedure, may its sacrifice not be in vain – learn more over at WTFMoogle