It's probably not possible with stock firmware.

You definitely have to have encryption enabled beforehand, as switching it on takes around an hour and cannot be intercepted. And encryption forces you to have a secured lock-screen normally (stock firmwares).

CyanogenMod7/9/10 has a unique Profiles feature; I was able to set up one with a disabled lock-screen. You can switch between profiles rather quickly (long-pressing the power-button brings up the power menu where one can switch profiles).

CyanogenMod users can read more here:
What are Cyanogenmod's profiles good for?
Certificate Install without mandatory PIN lockscreen
Android “fake having a locked phone” - Galaxy SII

It's probably not possible with stock firmware.

You definitely have to have encryption enabled beforehand, as switching it on takes around an hour and cannot be intercepted. And encryption forces you to have a secured lock-screen normally (stock firmwares).

CyanogenMod7/9/10 has a unique Profiles feature; I was able to set up one with a disabled lock-screen. You can switch between profiles rather quickly (long-pressing the power-button brings up the power menu where one can switch profiles).

CyanogenMod users can read more here:
What are Cyanogenmod's profiles good for?
Certificate Install without mandatory PIN lockscreen
Android “fake having a locked phone” - Galaxy SII