Sample mesh for usage in a grid

I've been playing around with the experimental Volumes nodes. My idea was to use a volumes velocity attribute to advect points. Which works now thanks to the Sample Grid node.

Now I'd like to store the colour attribute of the points back to the original volume. For which I can use the Store Named Grid node. But that only accepts grid values. See the attached screenshot from my node setup. I'm a missing something or do we need a new node to convert/sample mesh attributes to a grid?