Sure, but if this player is good enough to be worth a hand shake at the start of the season, they're already giving up money by playing in Europe rather than the NHL for most of the season, so why not all the money rather than some of it?
And if the worry of boosting teams this way is real, why aren't guys like Williams and Fisher subjected to waivers as well?
I can't help but think the answer to both of these questions is because it isn't really a real worry. There's not enough talent in Europe for this to be an actual source of major boosting unless players are deliberately doing it to help teams, and there's already a loophole if they want to. Maybe once upon a time this mattered but not now.
But then you could say Europe is not a major source of boosting because of that rule.
Veteran guys trying for a Cup in their last couple NHL worthy years would be best served by going to Europe and then signing with the established contenders than trying to guess who is a contender before the season. They are also best served by earning money and playing pro hockey than sitting at home (and maybe playing beer league hockey) waiting for March.