Add arguments to a IronPython CallExpression

Question

I'm walking over Python code with a PythonWalker. From the bool Walk(CallExpression node) method I want to add a argument to the call if it meets certain critieras. The node.Args is readonly and the property has no setter.

If PythonWalker are read only how do I alter code using IronPytjons PythonAst?

I'm using IronPython 2.7.x