CC1120 - WMBUS preamble problem

Hi

I'm setting WMBUS register: I've no problem for channel 1a to 3b, but for channel 0 (with modulation 4GFSK) I can't setup preamble register.

WMBUS standard says that preamble should be n x (AD), with n = 8, (equivalent to bit pattern 0111), so 32 bit long, but the only available values for last two bit (PREAMBLE_WORD) of register PREAMBLE_CFG1 are:

Bit no [1:0] Values:

00 : 10101010 
01 : 01010101 
10 : 00110011 
11 : 11001100 

How can I set the desired preamble?

Thank you