That avoids this problem, but results in a whole host of other problems. You’d be better off modding the engine and adding the functionality. It would possible hack in as another option that can be passed along with every element, or as a special option on every widget they can optionally push onto the paint stack when they are drawn.
The two places we do it are FSlateVertex’s constructor for pixel snapping the actual drawn verts, and ToSnappedRotatedRect when we’re pixel snapping the clip rect.