Well, that's decidedly not it, sorry. It was an actual written story.
Looking for a story
Are you 100% certain of the title? I've plumbed all of the old story sites I know of (Wren, Sickstar, Ladybumps, Overflowing Bra) and all of the old Yahoo groups of which I'm still a member.
I remember Sladky's old Expanding Horizons MSN group having a lot of stories that weren't posted anywhere else. If it were there, unfortunately it's probably toast.
95% sure. Do you have a link to the full Wrenspot story archive?
Wren Spot didn't have a ton of stories, and they were separated by expansion type. Just go to archive.org, search for www.wren-spot.com, choose a date and then browse to the body inflation section.
Could it be "Taking Hold" by Captain-I?
http://captain-i.deviantart.com/art/Taking-Hold-138614848
or "Revenge of the Balloons" by JB/Gravidlad?
http://gravidlad.deviantart.com/art/Revenge-of-the-Balloons-30634679
I definitely remember the story you're talking about, and yes that is the title. I'll scour the way back machine for the story.
I knew I wasn't imagining it - thanks. I've been looking too but haven't had any luck...
http://datgirlintogmod.deviantart.com/art/Night-of-The-living-Were-Balloon-471788048
the closest I could find. Maybe Wren knows? Cause the only page of Wrenspot that's stored in Webarchive is mentioned in Phantoncrow's post here:
http://bodyinflation.org/node/24463