>> So, is there a generic enough way to come up with a suitable transistor and resitor value to do this?

How technical do you want to get?

Current in mA through the Collector divided by the gain of the Transistor (see Transistors Datasheet) should give you the current through the Base. Pick a suitable Resistor to fit (5v out from the PIC less 0.7v for the Transistors Emitter/Base junction divded by the previously calculated Base Current). Example 50mA Collector current with a Transistor gain of 150 should give you a Base current of around 333uA. 4.3v/333uA=12.9K Resistor... drop down to next lowest preferred value=12K.

Alternatively fit a 10K Resistor in the Base which should drive most decent small/medium Transistors on the planet.