I have finally achieve a small dream for PM by "completing" a tool which compiles graphics directly to the obj format for the Epson tool chain!
This means that you can include the header files from multiple .c files, plus it also shoves alignment and positioning onto the linker so that you don't have to worry about it at all. The object files produced are also more space efficient than what the assembler produces, not that that matters so much.
Note that it's not completely tested and it currently only supports up to 3 colours. I'd like to eventually support more colours along with alternate gray calculation strategies, but not there yet.
Link here