Majority if not all times when I plug in my USB I want to use the USB Mass Storage functionality thus I was wondering there is a way to enable USB Mass Storage once a USB is connected.
Auto Mount Your SD Card should do that for you:
Automatically mount your SD card. Quit manually mounting your SD card every time you plug your phone into your computer.
I used that one one of my phones when I still connected it frequently via USB, and it did its job wonderfully. The app is available for free on the playstore, so nothing to lose :)