Well, all removable media I know of, that can be injected/mounted via IPMI is at least of type USB...although being of correct subtype floppy or cdrom, not of type disk/stick.
Also, entering the key manually via IPMI remote console on that server is also not an option (sorry, but I don't use bitlocker feature, all my servers are linux, encypted with LUKS/dmcrypt)?