Do you mean you want multiple vertex color sets for one mesh? More than just the four RGBA channels? I don’t think that is possible, even if you could I’m not sure how you would get access to them once they were on there since material nodes for using the vertex colors only give you access to the four RGBA channels.
If you have a model with multiple vertex color sets - you could UV the object and then use a program like Xnormal to convert the vertex colors into a texture and load that texture into UE4.
Feel free to explain what you’re trying to do also, maybe there are other ways to do it.
Hope that helps.