Twenty-five years ago I played with the same idea for some diesel-generators that were supplying a load with a very low power factor.
Today I would definitely try to use a separate LV motor to run up your generator. Even if there is a bit of the turbine in the way physically.
That way you would overcome the expense of installing a MV Variable Frequency Drive. Otherwise you would have to ensure excitation before accelerating, and that would be difficult with most modern brush-less excitation systems, and even with a brush-ed exciter you would have to adjust excitation to the VFD
Would you not have sufficient space near the non-drive-end of the generator to install this small motor? - Or maybe even building a small permanent magnet rotor around the coupling part from the turbine, and a surrounding specially built stator, supplied from a VFD? Some wind turbines use a technique similar to this.