Mixing a RelativeSource binding with a non-RelativeSource binding

[CyberBotX]

I've come across this situation that I am unsure if CalcBinding can handle as is or would need to be modified to handle (or if this is even possible with CalcBinding in any way).

I have 2 sources I want to do a boolean or on. One of the sources doesn't use a RelativeSource on it, while the other source does.

At the moment I am needing to use a custom IMultiValueConverter instead of CalcBinding.