It is not that these employees are external? Otherwise you could use expenses. Maybe you could assign the employees to the same user? How are they going to enter these timesheets otherwise?

Hi Josse! Thanks for your input. We had part time employees and would like to register project hours without adding new users. We pay our service provider for each user. Same user for multiple employees is not accepted by the system. Anyway, we got an agreement and have added limited users now :-)