Back in the 1990s, I was working in Kentucky for an ISP and doing assorted contracting work.
I had a case that was rather similar what you're describing, only ours wasn't run that way because of incompetence -- we were connecting up all of the offices of the Department of Public Advocacy, and for one location the state had decided that rather than get a new line to the DPA offices, as they were in the back of a shopping mall that already had some government offices in it, we'd get fibre pulled between the two offices. Mind you, this was frame relay and fractional T1 days, before DSL, so a new drop was pretty expensive. (I want to say it was around $500/month for just the line charges for a T1, not including the port charges to the ISP tht you were connecting through).
So, when we went there for the install, someone had already pulled the fibre -- I went on the 3 hr drive down there, got soeone to escort me to where I needed to go, and plugged in all of our gear, then went and set things up on the DPA side.
All was fine for a year or so, then we got a call that things were down -- we tried everything that we could over the phone with non-IT folks (it's an office of lawyers), so I was sent on the 6hr round-trip with spare fibre patch cables and such.
A quick check in at the DPA offices showed nothing wrong over there, so I went over the other end of the bulding. I don't remember what the name of the department was, but it was a sort of family services type thing (where people got food stamps, stuff like that). I went up the counter and told the person behind the plexiglass that I was with DPA, and we had equipment in their wiring closet that I needed to get access to.
To which she replied, 'DPA is around the corner'. And I said no, I work for the DPA, and I need to get into your wiring closet. And she kept repeating that DPA was around the corner. I asked for her to get someone else. And I waited 10 minutes or so for someone else to come out front. Once she showed up, I spent a few more minutes with the 'DPA is around the corner' response until I *finally* got through to her and convinced her to let me into their closet. (mind you, this would likely have been considered 'social engineering' if I did it today, as I showed them no ID, being that I had none that said I did work for the DPA).
When I finally got to the closet, I saw that our box had no lights on it ... I traced the power cord down to a power strip that someone had removed all other things from, and taped over those outlets and written 'BAD' across it ... yet left our fiber tranciever plugged into it. I think I was in the room for all of 5 minutes -- it took me *way* more time trying to talk them into letting me in the room than to actually diagnose the problems *including* the time spent in the other offices.
So ~6.5 hrs to fix a problem, because the other office didn't care at all about our gear in their closet, as it would've taken them less than a minute to have moved everthing that was plugged into the known-bad power strip.
So I'd have to say -- no way in hell should you run cable to a private office. If nothing else, that office might close or move, and who knows what might be in there next (or if the new tenents want to remodel it).