Give a position law to a spring

Hi everyone!

I have this model on Simscape, this is a quarter car model model on symscape that i built for a project.

Now i have to give to the spring on the under side a position law to simulate a street profile. I don't find a way ot give the spiring that position law. I was thinking to use as can be seen in the image an ideal traslation velocity source block and to pass it the derivate from my signal wave ( positon that i built on Matlab) but it seems to not work.