What if instead you gave a vector such as "fly heading 240, intercept runway 27 (localizer/final approach course)" ? You aren't vectoring onto an approach - just pretending that the 27 LOC is just any other directional navaid. Then once established (or you observe the pilot begin a turn to the right to intercept), you issue the usual PTAC sans the T. Is that not possible/allowed?
Here's part of the relevant section from the 7110.65, which dictates our operating rules:The following provisions are required before an aircraft may be vectored to the final approach course:
1. The approach gate and a line (solid or broken), depicting the final approach course starting at or passing through the approach gate and extending away from the airport, be displayed on the radar scope.
Although regarding your specific question, in our facility, every localizer course is depicted anyway. We use your example on a daily basis, vectoring to intercept. It's a good way to get people lined up for approach before you're ready to clear them.
Back to the OP... if the FAF was defined by non-GPS methods (e.g. intersecting radials, an NDB), they may have expected you to find it that way. But more likely they just didn't realize you were appropriately equipped. With all that said, you can't be cleared to initiate an instrument approach from a FAF anyway, so I'm assuming it was to line you up for a straight-in visual.