You might try some of the techniques listed in technote mg65571, Removing Small Resistors and Capacitors from the Calibre xRC Netlist.The type of action you are describing is generally referred to as "netlist reduction".
You can also find some more general discussions in the documentation. In the Calibre xRC Manual, look for the topics "Reduction Techniques" and "Creating Smaller Netlists" -- these will point out some generally useful SVRF statements. Calibre Interactive talks about including/excluding nets (so that only the ones you care about have detail), and may also have reduction available under PEX Options > Misc > Parasitics to Output to RC Netlist. (I have not used the 2011.2 version of Calibre Interactive, so am unsure exactly what is in there. It is where I'd expect reductions to go, though, as most of the reduction commands do not change the parasitics that get extracted, but only how they are shown in the netlist.)
The specific commands discussed in the technote and the xRC manual are described in greater depth in the SVRF Reference Manual.