Hey
It looks like this has been solved with some newer release of Gainsight, which now has a “variants” option - through which you can send different email surveys to different groups of people. The docs are here. HOWEVER, it does NOT do it with a random A/B separation. You have to create a way to divide the group.
I found Dan Ahrens’ solution to this to be very good. It is laid out here in detail. In essence you’re finding the median of the length of an Account Name and then dividing down the middle based on that. Once you have this, you can use it to determine the variant delineator.