Ended up bending a cheap steel stay for the exhaust, and fastened it to the transmission, but no luck with the banging.
Just a few days ago, the STI mounts arrived!
Wasn't ballsy enough to do a home job so borrowed the local mechanic's hoist and did the mounts there. It was a surprisingly easy job to do!
Here are some pics.


There was still some engine movement, but it was markedly subdued. The rubber compound in the STI mounts were incredibly hard compared to the jelly-like soft stock ones.
There were no bangs or eerie knocking noises during the test drive, despite hard launches and such. WIN!
Negative points are increased vibration and noise intrusion into the cabin. All in all, I think it was a good thing to change the mounts.
Also, lowered the car ~10mm both ends, but this proved to be difficult with increased scrubbing at the front during spirited turns. Flared out the front bit of the guards which did seem to alleviate some of the scrub, but will probably need to run a bit more camber. An upcoming change of the stabilizers to reduce the roll in corners should help too.
I found that the lock ring on the right front coil-over was loose, allowing the case to rock slightly. This happened about a year ago as well, and I tightened it up but it obviously wasn't tight enough.
hehehe...all this time, I had been wondering what the loud clicking/knocking noise was!!!