There are no silver-bullet solutions for booting ISOs via USB. A silver-bullet solution requires doing "floppy emulation", which is something that can't be easily done in a general-purpose way. For CD booting, each BIOS has this functionality implemented differently. For USB booting, the bootloader has to figure out how to do this. MEMDISK and GRUB4DOS are the only ones I know that do floppy emulation.
But then you have to do CD drive emulation too.
The way almost all ISO=>USB booters work is to pull the pieces apart and make them work without floppy+CD drive emulation. But this requires intimate knowledge of how that ISO normally boots, and thus it can't be a silver-bullet solution.