The latest SeaBIOS git can now handle lzma compressed payloads in CBFS. To use, simply place a coreboot payload in the "img/" directory of the cbfs flash. For example:
./cbfstool ./coreboot.rom add-payload coreinfo.elf img/CoreInfo l
One can then boot the image by selecting it from the "F12" boot menu.
SeaBIOS does not yet support compressed option roms. The cbfstool doesn't seem to support this yet - support will be added to SeaBIOS as it becomes available.
To provide the above, an lzma decoder is compiled into SeaBIOS. This adds about 3400 bytes of code to SeaBIOS (~1600 bytes to an lzma compressed SeaBIOS image).
-Kevin