Good point.. And that would be covered by having the commercial rating (which many pilots get along with their instrument rating (many get commercially rated without an instrument rating))..
They only grey area is taking the co-worker along. He couldn't even technically pay you out of his pocket even with the commercial rating (if the flight is over 50nm). You'd just have to have an agreement that he was along for the ride. He is allowed to pay for 1/2 the plane rental and any other flying expenses, and I know this type of thing is common-place. It's just a matter of book-keeping ;)
Yes, I've looked into this a little; the bottom line as far as flying on the clock goes is that it falls under "furtherance of a business" or whatever the wording is. I wouldn't be getting paid to fly, and as long as everyone has their stories straight, although the FAA is not really keen on flying pax from A to B, as if a taxi operation, they could not prove the co-worker didn't just decide they wanted to ride along. In fact, if it's a round trip, I believe the "taxi factor" doesn't apply at all in their eyes. It is a gray area indeed, which is good and bad.
I probably couldn't have the company cut me a check equivalent to airline fare or whatever, but I could get something back by perhaps submitting it as an expense. And I know i could write it off tax-wise.
Regardless, I'd be content to pay the bulk of it (cash-flow allowing, of course) and just collect my day's pay at my usual rate.
I'll have to make sure, of course, that I know all the legal ins and outs before I do this, and it's probably not worth trying until I have my IR. Maybe a trip that I could feasibly make by car if I had to cancel the outbound leg due to weather, or one that ends with me returning over the weekend anyway...but I still feel that in the end, I'm just as likely to miss an appointment or get home late while relying on the airlines as I am to rely on my PPL.
The notion that a client may gripe ("why didn't you just send him on an airline?") is worth considering, but I'm not in sales or management, so I don't represent the company in that sense (meetings, etc.); generally all they care about is that the work gets done by the deadline. If I had to dig in my own pocket to get a last-minute airline flight , a train or bus ticket or rental car, I'd still probably spend less than the bulk of a couple days' rental on a club plane, and I'd still get there in time to do my thing.
Flying myself could be less-than-efficient sometimes, but I wouldn't have to check my bags and tools, stand in line in my stocking feet, or try to sleep in a chair at the gate... that's worth a lot to me. ;D