If I were you, I'd be weighing the cost of finding a fix versus the actual users you'd affect. I don't think there are enough users to justify trying to find a fix, especially because the description of the problem sounds like it may be a Safari 5 bug.
Safari 5.7 doesn't even show up on CanIUse for transforms3d
And Safari 5 is only 0.2% of interet users in April and that stat doesn't even show the split between Windows and other operating systems, so it could be even less.
I tried to find a version of Safari 5 to run in Virtual Box: Windows 8.1, but I couldn't even find it...