If such a global import is possible, it might destroy Matlab's stability. The imported functions without wildcards have a higher precedence than nested and local functions. With wildcards they are preferred to private functions also. So after a "global" import, all of Matlab's toolbox functions, which use function names, which match the imported functions by accident, will run unexpected code.
Therefore I assume, that such a global import is not possible. And if there is a method to do this, you should avoid it strictly, because it is a shot in your knee.
The import functions should not take a lot of time. For 1e6 calls I do not see a measurable effect. If you call a function much more often, check again, if it is really required to import the functions. Remember that you can call e.g. java.awt.Robot directly also without the need to import before. Creating such an object takes at least 10'000 times longer than importing the function, so if the code is slow, avoid to create the Robots repeatedly, but create one object and share it.