Ask HN: Launching a startup from within a "parent" company?

I'm currently gainfully employed at a smallish consulting company. I like the company and the owners a great deal, but I've got the startup itch. However, I know my company would be very sorry to loose me.

Rather than branching out on my own, with all the risks associated with that, it strikes me that it might be possible to reach a mutually beneficial compromise: I stay with my company, keep my salary (possibly with a pay cut), spend ~70% of my time on my own project, and we split the profits.

Advantages:

* Low risk (for me)

* Moderately low risk for my company (my salary is small relative to their resources)

* High reward for both (profit ceiling and distribution should be about the same as with a funded startup)

* Zero overhead - my company already has accounting & tax infrastructures, a nice office with plenty of space, etc.

* Easy pitch - my company knows I'm capable and motivated

Disadvantages:

* Loss of control (maybe not, with the proper contracts?)

* Hard to sell the company for an exit (maybe not, if structured correctly?)

It's worth noting that I definitely envision the "growing a profitable business" type of startup, as opposed to the "building buzz and exiting quickly" type. Though I'd definitely want to work something into the agreement where I could "buy out" the whole company once it became self sustaining, if I wanted to.

Any thoughts? Anyone have experience with this? What would you assume a reasonable ownership/profit distribution ratio would be for this kind of arrangement?

(using a throwaway account in case my boss reads this prematurely).

(edited for formatting)