At my last job, some of the Supermicro servers I worked with needed their SSD firmware updated. The hosting company's firmware update tool didn't actually update the SSD firmware (ugh) and it took forever, so I started doing the updates with remote ISOs, but some of the hosts had gone through the hosting company's tool which sometimes updated the IPMI firmware even though I didn't tell it to (double ugh). For those, I ended up loading the ISOs via PXELINUX's ISO loader. Kind of gross, but it got the job done -- might be an option for you?
Yeah, I think PXELINUX and iPXE are using the same kind of tricks to load ISOs like this (if anyone wants to do a writeup I'd love to read it). I think I'm going to have to dig in and understand the "redfish" API that also appeared with the update.
