How do I use 'Run Updates in worker threads' in blueprint animation

Hello,
I’m currently using a blueprint animation graph with a Blend Space 1D and a Bone Transform that use blueprint variable to change their behaviour. I want these to be optimise by using the Worker Thread. Unfortunatly, both of these transformation will trigger a warning if I use a variable in blueprint. I generated these variable in C++ using the BlueprintReadWrite UPROPERTY so I can linked them in the graph, but it is still considered a blueprint variable.

So my question is, how the hell can I access the parameter of the Blend Space ID and the Bone Transform via C++ so that I can use the worker thread.

If you are wondering, the reason I want so much to use that optimisation is that, right now, the effect that I want to achieve work, but sudden change from the user make the animation clip for a few frame that is noticable. This only happen, however, when other actor are on the scene that have Tick activated. If my character is alone, everything is synch up perfectly.