I purr with my tongue in calling contests and it scores well. Best to do a motor boat sound with the tongue against the roof of the mouth. After that is mastered, try it w/a diaphram. Then "throw" the sound into the side ofa "soft"cheek to soften and modulate it... hard to explain, but it works on turks too. Still, I prefer to do the slate when I am calling a bird for a partner...
-fsh