My question is why you wish to use 11s shifters with a 9s cassette.

If wheels are the issue, a few solutions are possible.

1) You may be able to do a cut-down cassette, so using 10 speeds on a 11 speed cassette (plus spacers as needed).

2) Some people have successfully machined the inner sprocket group to overhang to the inside, and fit the 11s cassette on an 8/9/10 freeehub. This is especially relevant with the larger rear sprocket sizes. This maybe especially easy to do for flat rear discs (zipp).