It is not advisable to support the engine/transmission at three points. The T5 should just hang out on its own. Your front mount and the two rear engine mounts are plenty to support the transmission.
The best description of what happens with 3 mounting points I have heard, is that it is like holding a tree branch by the ends and putting your knee in the middle. Its easy to break. Just using your 2 hands on the ends of the limb, not so easy to break.
Carl
