Wirelessly posted (BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
If the availability is there (and that's a big "if"), one could also fly to PPT on LAN from SCL. You would fly AA/LA from MSY to SCL (with a connection in DFW or MIA), and then LA to PPT. The MR and UR points could be converted to BA Avios, which could then be redeemed for travel on both AA and LA.
LA does not offer First Class, but its Business Class is supposed to be excellent. And when redeeming BA Avios, you are entitled to stop over at your connecting points for no additional Avios.
You might also consider getting some AA miles via the Citi credit card sign-up bonuses which are detailed in this forum. Since both the AA and BA programs offer one-way redemptions, you could conceivably use BA Avios in one direction, and AAdvantage miles in the other.