How to save Ditamap as "book xx.0 with fm components" using ExtendScript?

I'm trying to write a ExtendScript Toolkit script to save a diamap file as a "book 11.0 with fm components".  When I do this manually I check the box "Prompt for Dita Val File" and select the appropriate Dita Val File.  In the code I've written so far I can open my dita map and save it as a .book file, but I don't know how to give it the location of the Dita Val File.  Anyone know how to add that to my saveParams?

var sourceDoc = openXmlFile("FilePath to diatmap goes here");
var path = "Output FilePath goes here";
saveToFm(sourceDoc, path);
function openXmlFile(filePath) {  
    var file = File(filePath);
    var fileName = file.fsName;
    var openParams = GetOpenDefaultParams();  
    var retParams = new PropVals(); 
    
    var doc = Open(fileName, openParams, retParams);
    return doc;  
}  
function saveToFm(fileObject, savePath) {  
    var saveParams = GetSaveDefaultParams();  
    var i = GetPropIndex(saveParams, Constants.FS_FileType);  
    saveParams.propVal.ival = Constants.FV_SaveFmtBookWithFm;  
    var saveAsName = savePath;  
    var returnParamsp = new PropVals();  
    fileObject.Save(saveAsName, saveParams, returnParamsp);  
}