I'll piggy back on this thread.
Similar situation: BKK-SIN on LX, SIN-LAX on United 12 hours later (but next morning).
I'm sure getting bags sent over will not cause a problem, but how do I get a BP as checkin for UA's flight generally doesn't begin until the wee hours of the morn. Id like to stay airside, but I can't get into the *A lounge without a BP so what are my options?