This is an interesting question. I have been involved in several projects that were governed by the API 1104 code, but have never encountered this issue.
I looked through the 19th edition briefly and in my opinion, what you desire is not authorized by the code.
To do what you want, you would have to qualify the welder for open root welding, in accordance with either 6.2 (single qualification), or 6.3 (multiple qualification). Once qualified, you can make assignments for who does the root and hot passes; and who does the fill and cap based on whatever criteria you want.
If I'm wrong, someone will correct me.
Charles