Alternatives to using Memdisk?

[nappington]

We currently use memdisk as the kernel to load BIOS update images in iPXE to perform BIOS updates. Unfortunately memdisk doesn't seem to work for Lenovo BIOS updates (ISO or .IMG) in any combination or permutation of arguments - the image loads fine, but whenever the actual update is attempted (Selecting "update system program" from within the update utility) the machine hangs entirely.

I'm wondering if there exist any memdisk alternatives that we can use to make the Lenovo BIOS updates work.