Is it possible to book an open jaw flight on LAN where the long haul is in Business Class but the other flight is an economy-only flight as a single booking? I haven't figured out how to do it on the LATAM site. And that's only kind of open-jaw I can create without adding half a day extra to my travel.

I would be considering flying LAX-LIM-CUZ if I could get not much more than half the price of LAX-LIM-LAX, given that I already got an AA miles reservation for LIM-LAX and thus don't need to buy the LIM-LAX direction. But LAX-LIM one way in Business Class is 2x the cost of LAX-LIM round trip !