You can’t set different overflow values if one of them is visible; the CSS3 Box Model draft says this in section on overflow: “The computed values of ‘overflow-x’ and ‘overflow-y’ are the same as their specified values, except that some combinations with ‘visible’ are not possible: if one is specified as ‘visible’ and the other is ‘scroll’ or ‘auto’, then ‘visible’ is set to ‘auto’.”
Regarding workarounds, you would first need to decide what the desired behavior is. When you have a scroll bar on the right, how would overflow-x: visible work? Should the overflowing content continue on the right of the scroll bar somehow? This would be difficult to arrange. Or should the scroll bar move to the right?
