I think that you can use the 'MATLAB system ' block, you can define a system object to compute the coriolis matrix.
There are two advatages:
Firstly, more efficient. You can invoke the internal funtions of Robotics System Toolbox which is more efficient than the outer function. And you can invoke the internal properities of rigidbodyTree object, which is convenient for coding.
Secondly, you can import the rigidbodyTree Object of a parameter of the block, which avoids invoking the importrobot function.
But the 'MATLAB system ' block is more complicate and you may pay some time to learn how to use it.
By the way, if you find a more efficient algorithm to compute the Coriolis Matrix, please let me know, and I will be appreciate. My email is email@example.com