Another thing you might consider toying around with Alex, is a "grrrr" type of flutter....perhaps even ONLY as you get really soft. Kind of switching from the tongue flutter to the grrr. I don't personally do or like the grrr or growl type way of getting this sound...but, maybe it's something that will work for you. I know several folks (especially trombone players) who use this tactic when flutter tongue is called for. That said...I am certain that with conscious practice, you will have "no problem" with whatever way you choose.