I don't know how soon the 64-bit version of TG2 will be released, but perhaps it's an idea to wait for it.
If you can't wait then there's a way of doing it by rendering it in crops.
You could render it in 4 crops, in this way for example:
crop #1
crop left = 0
crop right = 0.28
crop #2
crop left = 0.24
crop right = 0.52
crop #3
crop left = 0.48
crop right = 0.76
crop #4
crop left = 0.72
crop right = 1
With this setup all the crops have the same amount of overlap. This overlap is necessary to be able to remove GI-seams, which might and probably will occur. Though that depends on your scene of course.
Don't forget to use the ray detail region padding to allow terrain/objects outside the crop cast shadows/reflections into your crop-render.
I'm always a bit confused which setting to use, but I believe you need to use the "detail in crop" function.
You can set the value to 1 for example, which means that the shadows/reflections will be calculated 100% of the cropsize outside each size of the crop.
So with a 2500x2500 crop this will mean that shadows/reflections will be calculated in an area of 7500x7500 pixels.
You can imagine this is rendertime laborous, so a value of <1, 0.5 for example, might work as well and even faster.
Like I said again, it depends on your scene whether you need this really much. Perhaps you could post a smaller version of your image to show?
Cheers,
Martin