I think we could make it work for the plant swap without Dave doing any tweaking, but it would be clunky... we'd just have to use that comments field to make it clear we were talking about a seedling or plant division, not a packet of seeds.
I wonder if duplicating the tool and changing it just a bit so it's plants rather than seeds (two separate swap tools) would be easier than adding more options so the same tool can be used for both plants and seeds... ?
Our group has done an increasing amount of pre-event swapping by using want/have lists. We create a separate thread where people make ONE post apiece with their lists, editing them as needed. We have another thread for discussion and requests. By swap time, a person's post might contain a list of "haves," a wish list, a list of promised items, and a list of what they hope to receive. That takes a lot more editing and effort than using something like the seed swaps tool!