The easiest approach is to include a text field formatted with that value list as a match field in the portal's relationship.
Say your current relationship looks like this:
Employee::__pkEmployeeID = TimeOffLog::_fkEmployeeID
if you change that relationship to be:
Employee::__pkEmployeeID = TimeOffLog::_fkEmployeeID AND
Employee::SelectedTimeOff = TimeOffLog::Type
Then you can format SelectedTimeOff with your value list to filter your portal to show only records from TimeOffLog of the selected Type.
If you set up SelectedTimeOff as a field with global storage, you can select this option on one employee record and see the same type of records in this portal as you move from employee to employee record without needing to reselect the desired value.
Note: Since you may be using this relationship for more purposes than this portal. There is a good possibility that you'll need to create a new Tutorial: What are Table Occurrences? of TimeOffLog to use for this relationship and on which to base your portal.
For an explanation of the notation that I am using, see the first post of: Common Forum Relationship and Field Notations Explained