USB drive bootloader that redirects the boot process to an ISO image

I'd like to have a bootable USB drive that contains a boot loader that can prompt to select an ISO image to continue booting from.

In this question I've already provided an answer containing a tool that allows to write multiple bootable images and to select the one to boot from. The problem is that this approach involves writing all the images at once upon which it also compiles and hard-codes the boot selection menu in, so any modifications whatsoever require to burn the whole thing again, which is tedious and hard on the low endurance flash memory.

So I am looking for a solution that allows seamless adding and removing of ISO images without having to do any other modifications, instead of having the boot selection menu choices hard-coded in the USB bootloader, it should list the available images for selection.