However, since I bought each flight separately, I am not in transit when arriving the US and that will force me to cross the border through LAX, get my bags and wait some hours to take my next flight.
This actually makes no difference, because in the US, everyone connecting has to clear the border, and have the relevant visas to do so. The only difference is that with seprate tickets, you can’t drop the luggage at the dedicated belt before exiting customs, but have to use a regular bag drop desk.
So just write “in Transit” on the form
Since you’re in transit, just write “in transit” for the address, and show your connecting flight’s ticket if asked.
For what it’s worth, this is a common scenario that immigration officers will have seen before, because the US does not recognize the idea of sterile transit: every traveller has to pass through Customs & Immigration, even if they are continuing directly onto another flight out of the country.
Credit:stackoverflow.com‘