I understand that you want to select only few variables, while deselecting all other variables in the Import Wizard. But as of now, deselecting all the variables in a single step is not possible.
As a workaround you may consider using load to import specific variables from .mat file
For example, to load the variable named X from durer.mat file, these statements are equivalent
load durer.mat X % command form
Or
load('durer.mat', 'X') % function form
Hope this helps!
