Since the typical stalling (critical) angle of attact (aoa) for an average aerofoil section is "about" 14-16 degrees, now consider the average pitch of a propellor. I'd say its around 7-9 degrees from the plane of rotation(guess). So even if at a standing start, max RPM was suddenly applied, the blades would only reach a max aoa of 7-8 degrees. So to answer your question, to stall a propellor, you must exceed its critical angle of attack.
To do this, wait for a suitable gale (not long..uh winter's still with us) and park you aircraft facing down wind. Now fire up the engine, and with the initial reverse flow(depending on how intense the gale is), the blades should be operating at idle rpm, well above thier critical aoa, and hence they are stalled.
I hope that this has answered your question!??
Mr L