Hilton is having a sale which stacks really well with the current Amex spend $400, get $120 back deal.
For example, I was interested in staying three nights in the Sydney Hilton (King Hilton Executive Room) and before the sale, each night was ~AU$483 but dropped to AU$356. Please note that these sale prices are non refundable and they will charge your CC ASAP (which is what you want to be honest as the Amex deal runs out on 30 June 2018).
To be able to split the payments, you can do it a few ways. Probably the easiest way is to just call the Hilton and ask for in-house reservations (so you do not get an overseas operator as they cannot split payments across multiple cards) and just tell them the nights you want and be honest with them and tell them that you get $120 back for every $400 you spend and so that is why you are doing it.
I would make sure that you check in the App what the individual prices per night are as sometimes when you get a quote for multiple nights, the summed up nights somehow ends up being greater than the individual ones. If this is the case, just book (via the APP), Night one on CC1, Night two on CC2, and THEN call the Hilton In-House reservations to get the third night and split then (that is what I did).
For me, I ended up with three nights (Fri/Sat/Sun) for a total of $999.90 less $240 from Amex (or $759.90 for three nights with Executive Club).
Any Hilton's in Noumea? And would this also attract the AMEX deal?