Imagetransformation after cv2.stereoRectifyUncalibrated

edit

I am using python 2.7 and OpenCV 3.2.0 for uncalibrated image-rectification and dense stereo matching. My problem is now after getting my transformation-matrices with

cv2.stereoRectifyUncalibrated()

I don't know how to proceed and create my rectification-maps and do the remapping. I know that in the calibrated case I could use

cv2.initUndistortRectifyMap() 'and' cv2.remap()

The problem is I don't have a calibration matrix that cv2.initUndistortRectifyMap() needs and so my question is, if there is a workaround with openCV or do I have to write a function myself?