So, what if "moving" the island is not about a physical relocation, but about a relocation in time?
::dan::
NICE!!!!!

Well then, Widmore would still be able to find it, wouldn't he? The Island still being in the same Three Dimensions, albeit not in the same Fourth.
Unless of course, you mean that The Island would no longer exist in the present but somewhere in the future (ie. several years into the future). If that were the case, Widmore could still just wait for The Island to physically manifest at the time of it's destination.
IF he meant long term saving, like "how do I save the Island from Widmore forever."
I think he meant short term, "How do I save the Island RIGHT NOW from the crazy merc who's gonna burn it!"