Mark,
I'll try to stir things up.

If you separate the piloting from the airplane rental/ownership, you
may be able to meet part 91. The company would need to own or rent
the plane, then hire you (or others) to pilot it.

In this case the company (your customer) is in direct control of the
risks, and the general public is not put at risk.

Now all your customers could go together to buy some airplanes
(fractional ownership), then each could hire pilots to fly them, and
stay part 91.

As soon as you provide both plane and pilot, you could be perceived as
part 135.

Mitch Williams - Considering a 135 single pilot operation
certificate....