Wirelessly posted (BlackBerry8530/5.0.0.601 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)

Although it might violate LAN's contract of carriage (you'd have to check), the conventional wisdom on FT is that as long as one does not make a habit of it, the airline will not bother you. But frankly, even using 12,500 miles instead of paying $300 is still a decent redemption rate.

Are you using DL miles to get to and from S.A.? If you're paying cash, you might check what a "triangle" ticket -- which would include the SCL-EZE leg -- would cost. It might be considerably less than buying the leg separately.