I take it you are using the HR expense module. Each employee who will be entering expenses are required to have a home address in their employee record (HR - Employees). You can use the same address as the one in the user record if the employee is also a user. Once you have that done, you will be able to generate the entries. The Accounting entries will create a payable to the employee at this point, but you can change the partner if you want, then you can post your entries.

I hope this helps