The recommendation for dry yeast is no starter. There is ~200 billion yeast in an 11g dry sachet which should be good for most beers up to about 1.06x. If you do a higher gravity than that then the recommendation is to use two packets.
From my understanding, the manufacturers have built in A) twice the number of yeast in these than a liquid yeast, and B) glycogen reserves into the dry yeast balls. This means that you should have the proper size pitch amount of yeast cells and those yeast should have plenty of reserves to perform a healthy, vigorous fermentation. Putting dry yeast in a starter may only deplete their glycogen reserves and the starter would need to be very large to feed that kind of yeast population (think of a 5 gallon gallon starter here <-- that's your actual beer