There is no way, as far as I know neither officially nor undocumented.
Instead of coding the unwanted outputs by the tilde, using a clear and clean input argument is better in my opinion. It is much better to see the intention of the programmer eplicitly than a smart and fancy way to hide this inside intelligent parsing.
If you see a foreign code, or a code written by your own some years ago, decide what is nicer:
opt.OutputX_wanted = false;
y = myfunc(x, opt);
In the first case you can imagine, that myfunc can save some time, in the second this is not expected by experienced Matlab programmers. Although if the 2nd method might save some lines of code or some microseconds of run time, the debug time rules.