Form a lead tingle. A strip of lead ideally code 4, about 1" wide and twice the length of your tile. shape it so it hooks over the batton (ideally nail) and then position your tile on the roof. Wrap the lead up to support the lower edge of the tile so that it lays underneath teh tile. This method is usually used for slates and your tile may be too heavy but for a temporary solution then worth a try. If your nails are corroded, then likely to be across the whole roof so you should get someone professional to look at it as it might be more serious than a couple of slipped tiles.
j Williams
July 2008