a good idea that someone suggested to me was to blue tac a copy of your birth plan to the door of your room so that any new midwives (shift changes, etc) will see it. i also plan to go in with mine a few weeks in advance and discuss it (make sure there are no show stoppers that "are against hospital protocol, etc") and get them to put it in my notes. I'll also bring in multiple copies and give out to anyone that deals with me when i'm admitted (and talk through it with them to make sure that they are happy with everything on it)...
but i think that you're all right that the most important thing is that your support person understands the birthing plan and is able to advocate for you during labour if you're a bit too preoccupied or tired to do it for yourself... as long as my DH clearly understands the birth plan (which he will because he will be forced to help me write it!), then i think that making sure that enough people get hard copies of it is more of a nice-to-have than a necessity...