Mixamo Skeleton to do Root Motion Animation

So, for my entire project, I have been using the mesh and skeleton assets from Mixamo for my main character, which does not have a root bone. So now since I want my character to be able to roll, I downloaded the roll animation asset from Mixamo, and I have successfully modify the animation so that the animation now moves with a fake root bone created using the Mixamo converter, and hence get a new skeleton asset that actually includes a root bone. But now i’m lost, I realize I can’t just retarget the new skeleton to the old one since the old one, which comes from Mixamo, does not have a root bone in the first place. So what should I do now? The only way I can think of is to recreate every animations and set up my main character blueprint again with the new skeleton, but this can be a huge pain.
Does anyone know the best option at this point?

Update: I have manually set up both my skeleton (with and without root bones) animation retarget to humanoid, but the only one I cannot do is the root bone for my skeleton that does not have a root bone. I have tried to add a virtual bone to my skeleton but I don’t know how to move it, I guess I probably can’t?