@Macros,

How about patching the u-boot binary to replace "bootmenu.scr" with, say, "bootmenu.xcr", so that it will not find the expected file in your eMMC?

It's just one byte, at position 0x0002e380 of u-boot-2020.12-pali.bin, or 0x000233c6 of u-boot-2013.04-2.bin (replace "s" with "x")...