its a really easy mod
all you need to do is swap the wires that go to the tone pot from the switch, no need for extra capacitors on anything like that
here is a standard strat - pay attention to the switch

swapping the wire thats red in the diagram to the empty lug will now give you a tone for bridge and neck but none for middle

if you wanted two pickups to share a tone pot, just connect the relevant lugs together. This diagram shows the neck with its own tone and teh bridge and middle pickups share the other tone pot

the same value cap will be fine - but if you wanted a different value cap for each tone pot you simply wire them both like the one with the cap - going straight to the switch rather than linked together