Moblite 7 1S 450 to 300

I've got the WS Moblite7 that has the battery tray for a 450, but it flies much better on the 300s.  I saw this design and realized that it would help to secure a 300 battery without giving up the flexibility of running 450s when I would prefer more run time at the sacrifice of performance.  The tabs are set for the larger square battery, but if you just push the piece up, the battery will stay in place and you're all set!