How to model the intial value of a linear system using Simulink?

I have seen more than one examples presented in tutorials to show how to model control system in Simulink, most of which reads as below:

r->sum->PID->system Transfer Fcn->y | | -----------------------------------------------

But since transfer function assumes that the initial value in systems should be zero, how can I model a system with intial values together with the transfer function in Simulink?

for example, I have a state-space model like below:

x' = A*x + B*u y = Cu

assuming it is a SISO system, and x(0) should be considered, after I use the ss2tf() function to transform it into a transfer function, then how can I include the x(0) in the Simulink? Considering a case that there are lots of nonlinear parts in the whole system, a simpler treatment using feedback() or lsim() can't work.

Thanks in advance!