One of my customers has found a much simpler solution : adjust the power settings in the CC2500 configuration.
In the file LivingColors.cpp
The lines :
// write power setting to PATABLE memory using single access write. See table 31 on page 47
// of datasheet
De value 0xA9 can be changed to 0xBB (-2 dB output power), 0xFE (0 dB output power) or 0xFF (+1 dB output power)
The registers of the CC2500 are described in the datasheet page 47, table 31.
The updated library can be found here : LivingColors.zip