Using Partition Manager created partitions for FatFS

I have an issue with using partitions created by PM in external flash. I can create a partition in my prj.conf file and use that and everything works. But I need to put some data into the external NOR memory. PM creates the partitions correctly as far as I can see. But I have not found a way to make the FatFS driver correctly find those partitions. Basically I have the exact same issue as in this ticket:  How to reference PM generated partitions from device tree? 

I need to create a disk like this for FatFS driver to find.

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/ {
msc_disk0 {
compatible = "zephyr,flash-disk";
partition = <&external_flash>;
disk-name = "NAND";
cache-size = <4096>;
};
};
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

If I have the partition in internal memory I can at least make this compile (the partition is tiny so it won't work for my application)

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&flash0 {
partitions {
compatible = "fixed-partitions";
#address-cells = <1>;
#size-cells = <1>;
boot_partition: partition@0 {
label = "mcuboot";
reg = <0x0 0xc000>;
};
slot0_partition: partition@c000 {
label = "image-0";
reg = <0xc000 0x72000>;
};
slot1_partition: partition@7e000 {
label = "image-1";
reg = <0x7e000 0x72000>;
};
scratch_partition: partition@f0000 {
label = "image-scratch";
reg = <0xf0000 0xa000>;
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

The external memory itself is fine and I can read/write it with flash_area_read() and flash_area_write() functions. 

Is there a way to reference the PM created partitions from within the devicetree file of my main application?