Basically, most of your suggestions could just be done by anyone who feels the thing is important(e.g. you and the other guy you mention). Just buy tags in advance(eventually find a sponsor as 4000 tags will sum up to quite a bit), appear to FOSDEM and place yourself on the infodesk as volunteer to do exactly this task - handing out these tags and pens to write names on them. I hope/assume you will happily get some place on the info desk to do it, otherwise place yourself in the entrance of each building somehow. Should be doable.
Sure; 'patches welcome'. I guess I'm not as sure of your hope/assumption; I had the sense from Benjamin Henrion's email that a previous patch was rejected, and I wanted to know if the patch was rejected because it was incomplete and ill formed, or if such a patch will never be taken in :-/. So let's make that my basic question: if a group of volunteers built a name tag generating web site, and arranged the production and distribution of lanyards and blank name tags, would such an arrangement be accepted and affirmed? Because it would require some integration with main stream FOSDEM (messaging on the web site, and room at info desks). Cheers, Jeremy