Scaling using reference point?

I am trying to scale a group  of two circular objects with a reference to the centre of one set of pie shaped pieces. How can I do it using the scale tool? The scale tool either asks the percentage or if I try to do it the other way, it distorts the shape in a disprportionate way and never asks for a reference point. How can I scale using the reference length of one of the objects as marked in the screenshot?