Adding LS-120 support to the BIOS isn't going to be easy. Everything I've added has come from freely available code (Smart Boot Manager and some code contributed by Programmer), or from small patches to work around a few crippling problems. This is intentional, as I want the BIOS to be as legal as possible in all IOpeners that use it.
It *might* be possible to refresh the whole IDE Device List by using Smart Boot Manager's "scan" function. If I recall, this function was supposed to overwrite the IDE drive table that the BIOS detected. I never got the scan function to work right on my test machines, and I haven't had the time to dive into SBM's source code to figure out why.
The only other way to do this is to pull in BIOS code fragments from a similarly equipped machine, to create a sort of hybrid BIOS. I've done a few experiments along these lines (the "Special Edition" BIOS for added LCD support), but I could never get the onboard sound working in the hybrid, and I could never get the hybrid to boot without pre-loading the CMOS with "known-good" values before hot-swapping BIOS chips. Those problems pretty much ruined the experiment.