compact routing that extends the core area (encounter + nanoroute)

Hi,

In my design (4 metal layers), it happens that wires are routed not only
over-cell but also outside of the core area where the cells are placed.
This is, at least to my knowledge, not a real problem. However, these
wires are not routed as close as possible to the core area.

Does anybody know of a command or an approach to achieve a compaction of
the routing so that it is moved as close as possible to the core area
(maybe as post-routing optimization)? As mentioned in the subject, I'm
using encounter and nanoroute and I want to stick to these tools.

Thanks,
-Thomas Popp