Initially when choosing between Ko or BB I made a small experiment trying to tie them up together. It seemed to require a lot of glue code to actually make things work. I guess I haven't been trying hard enough. Someone ultimately got these two frameworks work in sync with this full-featured Backbone-Knockout bridge: http://kmalakoff.github.com/knockback
Looks quite promising although it doesn't seem to have any users at the moment.
Can I ask which plugin you are referring to? I've been looking for something like this.