Product segment in Expense claim

We want to forse user to enter a value in a particular accounting flex field segment. Right now this segment defaults to 0 in the template so the users do not select it. How can we do this. I was trying to enable the segments under 'Internet Expenses Setup and Administration' responsibility Internet Expense Setup screen but it is not working. To give you a scenario our setup is as below..

We have 6 segments in our chart of accounts

company.department.account.crc.product.future

company  is fixed

department is tied with the employee in HR

account is hardcoded in the expense template