Pencil trick doesn't work on the Block Erupter USBs; they have a forced oscillator speed so you need to swap the oscillator AND change out a feedback resistor.  There's a thread where someone did do that on here somewhere and a guy was selling kits to get them up to almost double speed IIRC.

The pencil trick mentioned here was for the Blue/Red Fury USB miners based on the bitfury chip.  Just search "blue fury pencil mod" and you should find it.  The frequency of those is determined by the resistance at a key location which can be lessened by tracing a pencil around the resistor.  Fun stuff!