Benringer question

I just bought the standard Benringer mandolin and love it. (though I wish it had more blade sizes)

How do you maximize the amount yielded of a really hard root vegetable. I always use a cut glove, and can't seem to get the last quarter of a rutabaga or sweet potato (slicing for fries the long way) to go through the largest of the julienne blades. The food just gets stuck and I can't push it through. Pre cook the food? Grease the slicer?