In a large bowl, combine rice flour, wheat starch, salt and pepper. Set aside.
Drain and finely chop the shrimp.
Peel the white radish and grate it through the small holes of your grater.
Put the grate radish in a muslin cloth or a clean kitchen towel and squeeze out as much of the liquid as you can into the bowl.
Measure out the collected juices and add enough water to the juice to make 3½ cups.

Pour the white radish liquid into a medium pot.
Add the grated white radish and bring to a boil over high heat.
Cover, reduce the heat to low, and simmer for 5 minutes.
Mix in the sausage, scallions, and chopped shrimp, cover, and cook for 5 minutes longer.
Remove from the heat.
Slowly add the rice flour mixture and mix continuously until free of most large lumps.
The batter will be thick and sticky and a little lumpy.
Set up the steamer and bring to a boil over high heat.
Brush two cake pans with a little oil and divide the batter between the 2 pans.
Dip a spoon into cool water and use the back of the spoon to smooth out the surface of the batter.
Carefully place one of the filled pans on the steamer rack, cover, and steam for 40 minutes.
The other filled pan should be covered and left sitting at room temperature while the first one cooks, or it can be cooked simultaneously in another pot.
Remove the pot from the heat.
Carefully lift the pan out of the pot, place it on a folded kitchen towel, and allow the radish cakes to cool to room temperature.
Cook the other filled cake pan.
Un-mold onto a cutting board and cut into desired pieces.
Fry them on medium high heat in oil, until crispy and browned, about 4 minutes on each side.
Serve with oyster and/or hot sauce.