I use the burley bee for our dog (75 lbs), but I remember having to modify it to add room for him. It was a while ago, and I forget exactly what I did...but it involved unscrewing the base and moving bits backwards. My guess would be a similar mod, and then adding something like a kid's booster seat from a restaurant when the kids go in.

If it's a smaller dog I don't think any mod would have been needed.