P-channel MOSFET with variable resistance on the drain
There's actually (perhaps) nothing wrong with using a PNP BJT in this application. You just use a resistor that corresponds to the maximum collector current (minimum resistance). In your circuit above, 7.5K would be fine. Typically the voltage drop would be in the 50mV range or less. If ~0.05V drop isn't a problem then the BJT is fine. 

It's okay to use a lower base resistance than required by the collector current, just not larger (subject to other limitations, which don't apply here).