Preheat oven to 400 degrees F.
Dissolve the yeast in the water. Put the 2 1/2 cups of biscuit mix in a large bowl; stir in the sugar. Add the yeast mixture, stirring vigorously. Sprinkle the work surface generously with the remaining 1/2 to 1 cup biscuit mix.
Turn the dough out onto the surface and knead well, 15 to 20 times. Shape the dough as desired. Place on a lightly greased baking sheet, cover with a damp cloth and let rise in a warm place for 1 hour.
Just before putting into oven, brush rolls with melted butter. Bake for 12 to 15 minutes, or until golden brown. Brush the rolls again with melted butter while they're hot.