Multiple source specification distance range between two particles

Hello all,

How can I shoot 2 particles in each event with a range of distance (d) between them i.e. 2<d<6 ?
With a gps source macro file. Can I do that? To fell randomly in that range of the distance I define?
When I say multiple source specification, can I specify the distance from the other particle?

Thank you a lot in advance.
Kind regards