It depends on the data bit rate of your application. If you are dealing with GHz serial chain, you may have to ask a more-detailed model from the socket vendor.
It's better and safe that inserting a socket model in the circuit t instead of modifying original IC's IBIS model.
Assuming that you are working with current technology in the IC I/O buffer, you need a better model of the socket than what you can put in the IBIS file. You need a good simulation model from the socket vendor. It might be possible to make an IBIS PKG (package) model that adequately models the IC package plus socket. Another option is to use an EBD file to describe the socket. I expect that the BGA package is more complex than a simple RLC, too.