Unreal engine uses Y- Normal Maps rather than bump maps, there are two main ways to achieve this result, the first would be to unwrap the rim and place the alpha in the correct position on the unwrapped texture
The second choice you have is to map a plane the same with the alpha on and place it in the correct position
for both the above you will need to convert your bump map(alpha) to a normal map through a program like Xnormal photoshop plugin or ndo
They can then replace the vertexnormalWS node
Bare in mine as as unreal uses y- you might need to flip your green channel either in unreal or through your chosen converter as it stands the white area will stick out the black area will not