There are 2 options for replacing a broken ungrounded socket: Pull a ground wire from the panel, along the baseboard and convert to Schuko, or find an old ungrounded receptacle you've taken out somewhere else before, install it and have the customer sign a paper stating you just replaced an existing outlet and didn't install anything new. Until 1998 it was also legal to put in a main GFI and use Schuko receptacles without ground, but this has been outlawed in this major code change.
