Access to diagram within makeTwoWay converter function?

I have a binding where I want to do a quick conversion, but that conversion is related to the data from another node. I’d like to have access to the diagram here in order to find that other node and get its data, but I don’t see a convenient way to do it. How can I best access other nodes’ data from here?

new go.Binding('location', 'position', (data, obj) => {
    return transformCoordsForThing(obj)
  }).makeTwoWay((val, data, model) => {
    // would like to access the diagram to find myOtherNode here
    let {x, y} = transformMoreCoords(myOtherNode)
    // do some transform
    return { x, y }

In general binding conversion functions shouldn’t depend on other Parts. I’m not sure exactly what you want to do, but my guess is that you shouldn’t be using a Binding to do it.