I suppose a simple way, without getting involved politically, would be to stop using any service which is hosted in the US or by a company that falls under US jurisdiction.

A stampede of users leaving the likes of Google, Facebook, etc. would put pressure on those companies to use their resources to fight it 'at home'.

I realise this is a relatively naïve POV, but you only have to see how quickly Instagram reversed their ToCs a few months back - after users started closing their accounts in droves - to see how this can prompt the big boys into action.

You could also argue that there's a real opportunity for a European competitor to launch a rival to these services, under the guise of our strong data protection laws (in the UK at least). So if a DropBox or Gmail clone (for example) started to get traction, again it would put pressure on.