Carrier freezout actually makes this non-workable -- there's a limit to how cold you can make CMOS devices before they stop functioning. To say nothing of the specific heat of liquid helium, which is miniscule compared to LN2
Using a blowtorch as a heat-source is common in extreme overclocking, to heat up VRMs and memory modules up enough to boot the machine, and keep it working.
liquid helium might get into the device itself and cause other problems. (e.g. iphones stop working in the presence of helium)
