Hello,
well I understand what you want and does not matter how this is named. I do not play with a stepper for a while so I am not sure but I belive it is about a timing.
If you are able to change speed of the motor then you just need to do in you move function.
You need to a normal and initial speed. Then in your move function you need start from and initial speed and increes it with every step up to normal speed. And same thing vise wersa.
BR, Jan