Ok, then my assumtion was correct.
The correct register settings you find by setting Smart RF Studio as you described (Continuous TX -> Modulated (Modulation Format -> 2GFSK), Data format -> Random Mode)
PKT_CFG2=0x06 (random package)
PKT_CFG0=0x40 (infinite package length)
Write a byte to the TX FIFO
Strobe TX.