CC1120 Sniff mode with external 32.768KHz clock for better acurracy

Based on the CC1120 user's guide (Figure 1 block diagram at the left top) and 9.6 (Enhanced Wake on Radio). Can I use an external 32.768KHz (taken from external RTC clock) and feed it in GPIO3. Can I use it instead of the 32KHz RC clock so the sniff timing will be much more accurate i.e. 10ppm instead of 0.1%.