How to model bidir switch in RNM

I was wondering if there was a way of modelling bidir switch.

Using code, I always have a problem of propagating signal.

For instance:

module bidir_sw( a, b, ctrl);

inout a;

inout b;

inout ctrl

wreal a;

wreal b;

logic ctrl;

// this will only work from b -> a

assign a = (ctrl == 1'b1) ? b : `wrealZState;   

// this will only work from a -> b

assign b = (ctrl == 1'b1) ? a : `wrealZState;

endmodule

Is there an easy way to make it work both ways, using XCELIUM ?