Unlock the 4MB L2 cache is more likely an april fool lame joke to me ( they spread this rumour on april fool)
Allow me to analysis the situation to you

- You have to open the IHS in order to perform the mod on the circuit of the chip. In case they solder the core and IHS together instead of using thermal paste, GG to your proc.

- You have to understand the circuit. Also, all your efforts are wasted if intel lock the L2 cache through microcode instead of modifying the circuit. ( But chances that the cache is locked through the circuit mod are high )

- We don't know what's the actual reason why intel downgrade it to E 2xxx. There is high possibility part of the L2 cache are found faulty during the fabrication process, that's why intel lock the cache and downgrade it from E6xxx to E2xxx. ( Come on, we know intel. They love business!  They can sell these chips at better price if they let go them in E6xxx form what)

of course it is possible to unlock it , the chances of success are low and we don't know the L2 cache still can be used or not