[stereobit]

Does your startup have PMs and is looking for more? If so I would just ask if there is an option to switch. This is how I did it years ago. Shadowed one of the PMs for a bit and then slowly took over more responsibility.

[ryandrake]

That's exactly what I did. Watch PMs in action at your current company, take notes, get interested, and wait for a position to open up internally.