To add a reference to an assembly that is already in path, add a line beginning with //GAC: followed by the DLL names delimited by comma as a first line to your script.

//GAC:System.Data.dll

To add references to any other assemblies, add //GAC:System.Data.dll as the first line, and then add a line beginning with //ref: followed by the full paths to your DLLs delimited by comma as a second line to your script.

//GAC:System.Data.dll

//ref:c:\temp\myref1.dll,c:\temp 2\myref2.dll, c:\temp 3\myref3.dll