Thanks! Then it works as I had hoped.
I don't think the rules for this are very clear though. This is what the rule book says:
... almost all action spaces may be occupied by several players (Exception: Large City Cards actions, see page 11). If a player wishes to use an occupied action space, the following rules apply:
* The player wishing to use an occupied action space must pay for its use. The cost is a number of Coins corresponding to his lowest-numbered die placed at that action space.
(Text that says the dice should be stacked on top of each other.)
Exception: “The Favor of Khan” action area (see page 7) only has 4 total dice spaces available. When taking this action, the dice are never stacked on one another.
I think this text can be interpreted as that you may place a lower die on the Favor of the Khan action space and pay the cost, and that the only difference to the other action spaces is that you don't stack the dice but put your die on one of the free remaining spaces.