I'm afraid you can't do this yet on the SVC/Storwize family.
The common approaches to overcome this seem to be:
Both those options are non-disruptive. The first obviously requires that you have enough free storage capacity elsewhere to do the temporary "swing". The second requires that you've got enough new drives to warrant making a new array from them (i.e. not appropriate if you're just talking about adding a single drive).
here you can add an vote or make a comment for this needed feature