I've saved the riding pose, but I think it's time to try a side saddle position
View attachment 6376
So it looks like you decided to do the side saddle thing, but just an idea if you try to do something like that again (assuming this isn't what you tried). So in frame one, have the donkey below the ground level, basically out of the scene. In frame 20 or so you want to have the male figure posed so he is sitting with his feet straight out in front of him, but spread apart enough that they will go around the donkey. At this point you want to have moved the donkey up a little, but so that he should be touching the robe just yet. Next another 30 frames out I'd say, so like frame 50 you'll want the final pose, with him sitting on the donkey. If the donkey's a collision object, this should do a good job of moving the robe the way you want it. And I'd say probably have 60 frames total to let things settle in place.