Well there is something to be said for the rule of law, no?
I would suggest that the EU gets their ass in Gear and outlines a law that (narrowly) defines if and when frozen assets can be seized. For all I care they make a law specifying this time as a limited exception (but I could imagine several high level crimes like warcrimes could be added). Get it done.
I'd suggest adding a provision that if you want the frozen assets back you have to be personally present for a court hearing.