A snippet from the source code of my iPhone app, GRiS:

- (void) tableView: (UITableView*) tableView
willBeginEditingRowAtIndexPath: (NSIndexPath *) indexPath {
	// the mere presence of this method causes a swipe action to be
	// recognised, and a delete button appears. like magic!
}

I’m glad it was so easy, but fairly unnerved at the same time…