Filter by user? Dynamic filters?

I have a custom field on an entry form displaying options from a custom record.  I would like to set an Employee value on these records and use it to filter what is displayed by user (not by role).

I see how you would filter options by comparing against a *fixed* value, but that isn't going to help me here.  Is there a way to filter against a *dynamic* value (such as logged in user), or perhaps a value in the parent record (e.g. employee field of time entry screen)?

Thanks in advance for any help,

Dylan