Is hourly paid lecturing a viable route into a permenant lecturing position?
I would personally not do this.

The world is cruel so why should the institution you are at right now offer you a permanent position when they can get you are a discounted rate?
The perspective could change if you knew for certain that a position was to open in the near future, but even then I doubt you would just be “gifted” the position: there would likely be a formal competition with no guarantee that you actually get the job.
Indeed coming back to 1., if a position is open but the locals know you’re willing to stay, why would they hire you if a position comes open when you’ll still be around anyways?  They could get 2 for the price of 1 by hiring someone else if a position comes open.

Where I work contract lecturers have some sort of protection against outright exploitation (after a few years they have the right to first refusal) but these very very rarely get transformed into permanent positions.
Not that I agree with this way of treating people as human commodities, but then again... it would not be the first time the scenarios above actually happen.