I’ve come up with a solution, I set the character movement mode to flying during the sliding state with the impulse to mimic the gravity.
Note that sliding upwards and downwards has a different impulse force to help the character accelerate and launch off ramps, and make sure to have a speed limit and smooth acceleration, or you will be flying at Mach 10
The result is quite okay; at least I managed to make the inertia feel good and believable after tuning some force values.
Feel free to leave any efficient solution.