Derive Tax Registration Country from Taxpayer Country

In the external/internal supplier registration approval rules we can use the variable Income Tax >Taxpayer Country

But in the Spend authorization approval rules we only can use the variable Transaction Tax>Tax Registrations

>Country

We need use in the Spend authorization approval rules the same variable Income Tax >Taxpayer Country, because the spend authorized is automatically lunch after the internal register is approved.

How can we automatically derive Transaction Tax>Tax Registrations>Country from Income Tax >Taxpayer Country