Ah, so (this was also mentioned earlier by alec_t).
Then this scheme, using a P-channel device:...
would only work if the gate drive polarity was as shown (negative with respect to ground), is that correct?
I'm a little confused (polarities always do that to me). Isn't the gate polarity and voltage reckoned with respect to the source (the datasheet parameter is Vgs)? So does a P-MOSFET need its gate driven negative (with respect to the source) in order to turn it on?