We had a similar problem with the Advanced Repeater installer. There the documentation actually says that console and silent modes are not supported and I suspect that it may be the same for the RCP client.
I think it is fair enough that you need the X11 libraries for the RCP client install as you need them to run the console anyway. However, not being able to do a silent install is much more of a problem.
I am raising a ticket on the silent install issue for the advanced repeater and I suggest you do the same for the RCP client.