Not the most elegant thing to do in general but probably fairly safe here.
I believe C++ defines that elements within a single private/protected/public block will be in order. As FVector doesn’t have virtual functions you don’t have to worry about a pointer (typically at the start of an object, but doesn’t have to be).
/** Vector's X component. */
/** Vector's Y component. */
/** Vector's Z component. */
Given that X is the first element you could also go with: