[Proj] Little sphere projection

[Carlo A. Bertelli (Charta s.r.l.)]

Hello,
I'm trying a simplistic approach to a topological representation. I'm
mapping the possessions belonging to a group of abbeys in a regional
space. Il works well at a small scale, but when the abbeys are
clustered in major towns, the representation ties properties to the
cluster and not to the single abbey. The fact is that towns (and
clustering) play a significant role in this story (yes this happens in
the 18th century), asks for a better representation.
My idea is analysing each town cluster using a little sphere (or
ellipsoid) centered on the town whith an emisphere that only covers
the space of the region, so to show larger distances in town (so to
distinguish any abbey) and reduced distances far from the town center.
I think it should not be impossible to craft ad hoc projections, but I
have no idea on how to do it. Could someone help me?
TIA
c