It is not possible since those variables are only around while the JSP is executed on the server, when the javascript is run in the browser it has access only to what's in the returned html.
There is a workaround, what you can do is iterate flowScope in jsp code and write javascript to the html document. For each object in flowScope you output a javascript variable assignment. That way you'll embed the data in flowScope on the server in the html. It could be helpful to output it as a json structure where the global javascript variable is named flowScope and is an object with members for everything in flowScope.
In pseudo that would be someting like:
write var flowScope = {
foreach entry in ${flowScope}
write ${entry.name} = '${entry.value}',
write }