Related with Conditional Columns

We have recently implemented PowerBI in our organization and have been navigating around with DAX. Question is around RELATED function. 

In our scenario, there are two fact tables, say Sales Fact and Inventory Fact both joined to three conformed dimensions - Customer, Office Location, Region. 

Trying to create a conditional column in table view. Zone = IF Office Location = 'N/A' THEN Region ELSE Office Location. 

However, PowerBI is only allowing to create this column in either of the Fact tables. We want to have it in one of the Dimension tables so it can be used independently with either Fact table like any other Dimension attribute. 

Thanks for any assistance !

What is the best way to accomplish this? I know this can be done in Power Query but wanted to understand from DAX perspective.