The best way to do this, I guess, is to monitor files and folders outside of QlikView.
A small program or batch (CMD) file checks the availability of this file or folder. Upon detecting the right stuff, it sends an EDX request (there is a command line tool for that, see QMSEDX_commandline in doc http://community.qlik.com/docs/DOC-2650) to your reload task. Configure your reload task to also trigger on receiving an EDX request.
Now schedule your monitoring tool using Windows Task Scheduler to go and check with the preferred frequency and you're on your way.