That is very doable! The term to search on is "reduction". The actual commands have changed over various releases, so I cannot suggest the best ones for you.
For an overview, look for an appendix in the xRC User's Manual called "Reduction Techniques", or something similar. It was introduced in 2008, if I remember correctly. (If you are using an earlier version, there will be reduction information, but not all in one place.) In the SVRF manual, look for "PEX Reduce" statements. The 2010.3 version has 9 different reduction statements. (Very old versions of xRC had some reductions that did not begin PEX Reduce; they should be referenced from the main ones, though.)
Because the reduction methods change frequently, this is one case I highly recommend using the documentation that goes with your version rather than looking on SupportNet for the most up to date description.
For more help, I will need to know what Calibre version, what type of parasitics and netlist, whether any xcells are involved, if it is an ASIC, and what are the particular characteristics that you most want to preserve. If you do not want to reveal this information on a public forum (understandable), you could contact customer support.