Smart idea!
You have to think about a few factors though ... you're losing 2 pop and it takes a certain number of shields to build the settler in the first place, and then support him while he gets to his destination.
What i like to do as a small twist is make sure my culture puts nearly every other civ in awe of mine ... then i create a small city in one of those 'empty' spots somewhere in the middle of my civ (of if none of these exist, on the outskirts but still in touch with my borders) and give it to them in trade, and just wait until they rise up and rejoin my civ
Works like a charm so far - a dozen times or so in my last game ... just thought i'd let you know !
Cheers! and good gaming everyone
~Alex