I found no way to resolve this. There is no way of refractoring existing code as you expected.
But you can avoid writing such switch statement now onwards by enabling off/on tags as explained here Eclipse Formatter Allow Multi Line ; and then changing the switch template in Windows > Preferences > Java > Editors > Templates
as mentioned below
//@formatter:off
switch (${key}) {
case ${value}:${cursor}
break;
default:break;
}
//@formatter:on