First, if you are using the webserver, go into your QEMC >System >QlikView Web Services >Web tab and under RootFolders add the name AJAX and path to your AJAX generated pages. Now hit apply.
Now in the QEMC >Documents >User Documents >Select the qvw for which you would like to use the legacy ajax for and under Accesspoint access methods >AJAX Zero footpront Client Url:/AJAX/<yourqvwajaxfolder/default.htm . Then hit apply. Now when you browse your AccessPoint url and select that application for AJAX it will be redirected to your generated pages rather than generating them on the fly.
Alternatively (to first step) you can add the AJAX folder to your IIS as a virtual directory instead of in the QlikView Web Services section and if you are running the IIS & QVWS services they should share.
Hope this helps!