According to FitSharp issue 123 it wasn't possible to in July 2014. I was wondering if this has changed in the years since.
There's no way defined in the Slim protocol to do this. We'd have to inspect the parameter types to see if a method wants the Slim symbols passed to it, e.g.
using fitSharp.Machine.Engine;
...
public void GetTheSymbols(Symbols symbols) { ...}