Assignment of wreal nets without using ports

I'm trying to create stimulus that can be instantiated without port definitions in an AMS simulation.  I have been able to assign logical values in this configuration, but so far all of my attempts to assign real values to wreal nets end up converting the net to a logical net.

Example:

module test_stimulus();

//logical_net is correctly defined as 1'b1 in testbench_top.
assign testbench_top.logical_net=1'b1;

//wreal_net is defined as 1'b1 in testbench_top.
assign testbench_top.wreal_net=4.5;

endmodule;

The wreal_net is defined as wreal inside hierarchy of the testbench_top and is defined as real value "0" without this assignment (wreal default value).

Is there any way to accomplish this, or is is hierarchy connection the only way to assign real values to wreal nets?  I am hoping to simplify a stimulus strategy for large and dynamic verification environments without needing to constantly rework symbols, schematics, and port definitions.