Robert,
It should be possible, but please remember that European sockets are random wired for live / neutral polarity, so you would need to make absolutely sure that the live feeds were connected together. So you'd need to take some test equipment with you and do some simple tests before you connect up.
If you were taking the dual power feed from a single post, then both sockets should be from the same phase. Different posts may be fed by different phases - and you don't won't to go there.
And unless the second feed was free, you'd be better off paying for a 6 or 10 Amp supply.
Robert