How to add attenucation to simple circuit

I've been testing my line with a dsl router that I have. I would like
to know if there is a simple circuit that I could put together that
could increase the attenuation about 20 dbm. Connected to the frame
in the Central Office I get about 8 dbm I would like around 28 dbm.
Is there a simple way, for instance connecting 2 capacitors in series.
The phone line carries around 48-51 volts DC. I know it sounds
strange adding attenuation in this case, but I'm curious if it could
be done artificially instead of just being dependent on the distance.
If I test about a block down the street I get about 4 dbm more. Any
help would be appreciated.