Trying to remember what locates the grease washer, it may locate on a step in the stem OD. You actually could likely make one up out of thin metal plate or a big washer.
You actually can simply install a grease zerk in the head and fill the entire head with grease but the excess amount will likely leak oil when the grease begins to settle out in hot weather. One could put a loose (plastic?) collar of some sort around the stem to take up space to not have to use so much grease.
A clever mind has workarounds there.