How do I port a signal (reference data) from testbench to RTL module?

I run some encryption logic and wish to mirror some reference data from testbench to RTL module, 

exactly the opposite compared to what one would normally do to mirror existing singals from RTL to TB. 

The signal doesn't exist in RTL, I want to use TB to generate a singal in RTL and mirror values to it. 

Can that be done in ncsim or irun?