yocto do_unpack() - same directory names in different layers - yocto

Question

During experiments with Yocto's Advanced Kernel Metadata I got into a situation where I would like to have the .scc, .patch and .cfg files organized into a directory structure as mentioned in the syntax section, and to keep that structure in all the layers (consider 2 layers here - meta-main_layer and meta-bsp_layer):
meta-main_layer
└── recipes-kernel
└── linux
└── linux-yocto.bb
└── linux-yocto
├── cfg
│   ├── main_frag_1.cfg
│   └── main_frag_1.scc
├── features
│   ├── main_feature_1.cfg
│   ├── main_feature_1.patch
│   └── main_feature_1.scc
└── patches
├── main_patch_1.patch
└── main_patch_1.scc
meta-bsp_layer
└── recipes-kernel
└── linux
└── linux-yocto.bbappend
└── linux-yocto
├── bsp
│   └── bsp_definition.scc
├── cfg
│   ├── bsp_frag_1.cfg
│   └── bsp_frag_1.scc
├── features
│   ├── bsp_feature_1.cfg
│   ├── bsp_feature_1.patch
│   └── bsp_feature_1.scc
└── patches
├── bsp_patch_1.patch
└── bsp_patch_1.scc
meta-main_layer/recipes-kernel/linux/linux-yocto.bb contains:
FILESEXTRAPATHS_prepend := "${THISDIR}:"
...
SRC_URI = "file://linux-yocto;type=kmeta \
"
Edit:
And meta-bsp_layer/recipes-kernel/linux/linux-yocto.bbappend:
FILESEXTRAPATHS_prepend := "${THISDIR}:"
...
SRC_URI += " file://linux-yocto;type=kmeta \
"
... end of edit
This means that after parsing the recipes, the SRC_URI will contain file://linux-yocto;type=kmeta twice, and FILESEXTRAPATHS=meta-bsp_layer/recipes-kernel/linux:meta-main_layer/recipes-kernel/linux:. The way I understand it, the do_unpack() task goes through the files in SRC_URI and for each of them, it searches FILESEXTRAPATHS for that file, and it takes the first one it finds. That means that in my case, only the files from meta-bsp_layer are taken, as its path is the first in FILESEXTRAPATHS, and the files from the meta-main_layer are ignored.
What I would like to achieve is that instead of taking the files from only the first path found in FILESEXTRAPATHS, do_unpack() would go through all of the paths in FILESEXTRAPATHS and merge the directories of the same name (cfg, features and patches) from both layers. Without that, I don't see any big benefits of using the Advanced Kernel Metadata mechanism. Could anyone advise how to get this done?
PS: I'm using Yocto Zeus.