I’ve given MultiOut more thought this morning, and ran some tests. I have a design that would be quite easy to use with one #include for your custom program, another #include with the preprocessor magic. You would set the path of where you keep your includes in the first CustomExpression node, and chain additional CustomExpression nodes for additional float outputs. Your program will run first, outputting an array of floats of a given count, and the additional CustomExpression nodes in the chain will output individual floats from that output array. Only limitation in this easy-to-use design is that you would only have one MultiOut program per material.