(YES) you can turn off the phone without the digitiser, press the power button a the home button together for 8 to 10 seconds, this will either switch the phone off, or take you to a black screen with a apple on it.
if you get the Apple i the middle of a black screen then just hold both power ad home button of another 8-10 seconds
thought remember that the battery goes in to this phone before the motherboard; simply meaning that there will always be power going through the board, even if the phone appears to be off