I don't know if this could help or not because this seems so "been there, done that", but the best carrier I've found is the pet pocket. I can carry Pippa in it and walk Scout in comfort. I have also carried Scout around in it all day at a craft fair (it was raining) and it was never uncomfortable. Plus, as a bonus, you can dress up as a kangaroo at halloween and Hallie can be the Kit (or the Roo in Kanga-Roo...tee hee).
http://www.petexpressions.com/petpocket.html