Building a cassette only works with non-spidered cassettes. I'll re-space a cassette to match a shifter, typically 7 with an 8 speed shifter. But there is no magic in only running 8 speeds on a 9 speed cassette, if a person doesn't want to run the 11t. Either block it out or just don't use the 11t it and add a spacer to fill the gap.

John