Finally figured out how to provide direct path to config

Honestly reading the code is the best docs

linux/Makefile

@@ -0,0 +1,15 @@
+MAKEFILE_DIR := $(dir $(abspath $(lastword $(MAKEFILE_LIST))))
+
+BUILD_DIR ?= $(MAKEFILE_DIR)build
+ARCH ?= x86
+KERNEL_FILE_NAME ?= bzImage
+
+KERNEL_PATH = $(BUILD_DIR)/arch/$(ARCH)/boot/$(bzImage)
+KERNEL_BUILD_DIR=$(BUILD_DIR)/linux/kernel
+
+all: $(KERNEL_PATH)
+
+
+$(KERNEL_PATH):
+	@mkdir -p $(KERNEL_BUILD_DIR)
+	$(MAKE) -C $(MAKEFILE_DIR)/kernel O=$(KERNEL_BUILD_DIR) KCONFIG_CONFIG="$(MAKEFILE_DIR)/.config"