Multi Material Decoding with Unity Plugin

I try to decode Draco files with multiple materials on the same object.
I use --metadata flags to keep materials within encoding, but the Unity plugins seems to ignore that when decoding to Unity Mesh.
After mesh decoding I am using a MTLLoader to load the mtl library, but when I apply 2 materials to the decoded models, Unity says this models doesn't have submesh. The final result is that the 2 materials superimpose or something like that.
Is there a way to handle that with the Unity Plugin ? Or someone know how to split my obj by material before encode to Draco ?

Google draco is very interesting, but there's definitly not enough documentation especially about how to handle materials.

Thank you for your help