Resource Management - Combined functionality of FTE and The User's Schedule

Currently, we only have the option of using FTE with default schedule or user schedule without FTE. We need the combined functionality of both FTE and user schedule. For example, we want an engineer to be available 75% of his time (30 hours per week) to work on projects, but if he is taking 2 days off on a particular week, his available hours for the week should be 14 hours (30 hours - 16 hours). This functionality would make resource management a lot more easier.