Keep rolling and when you reach the pointy bit, roll over it so that the very tip of the point sits just underneath the roll. (alchemyinthekitchen.ie)
Using scissors, cut the very tip off the sandwich bag. (lovintheoven.com)
Otherwise, you could probably use a ziploc - type bag with a very small section of the tip cut off, or a piping bag with only the very tip cut off to make a small hole. (brighteyedbaker.com)