How Do I Allocate Home Office Expenses Between Two Businesses?

In the interview for business 1, I specify that I am using the same home office for another business. 
In the subsequent interview for business 2, I again specify that I am using the same home office for another business. 
However, I am not able to allocate the total expenses between the two businesses, e.g. 60/40. Turbotax just creates two home office deductions with 100% for each.