A friend is registered for Nation's Tri but cannot do the swim leg. I don't know if it's logistically possible or even race legal to share a bib, but I said I'd post to see if it could be done and if anyone is interested in just doing the swim leg.
Sharing bibs isn't really something that can be done in triathlon unless you are registered in a relay category - and I'm assuming your friend isn't. At this late stage, switching categories like that is next to impossible. Packets are already printed and shipped and a host of other logistical concerns are involved.
Hopefully your friend can find a way to get in the water and at least float the course. This is a pretty great swim, in my opinion, and it would stink to waste an entry.
I would encourage him to email them, they might let him do it as an aqua velo and just not be competative. It wouldn't have the same competition element but at least he would still be able to participate. (I can't find anything to indicate they would say yes, but it's worth asking.)