Our DynamicILInfo.SetLocalSignature() throws NotImplementedException.
Fortunately there is very simple example code that demonstrates how it can be used:
which I believe is so primitive that we can only write almost identical code to write Hello World.
Mono lacks an implementation of DynamicILInfo.cs.
Ideally we would implement ILGenerator on top of it and be done, but that's a big change.
As a workaround, use ILGenerator instead, which Jurassic has support for anyways.
We still don't have that method implemented.