Locked my key in the trunk of Lexus Ls 400, 94, any suggestions how to get the trunk opened

Locksmith but you should have a middle arm rest big enough for a kid to squeeze through which goes to the trunk directly in back seat

There is no pass-through to the truck on an LS400. You need a locksmith or extra set of keys. Does your LS have a remote truck opening button?

Yes it does under the dash board on the driver side

Yes

Yes my Lexus LS400 does have a remote on the left driver side by the knee

Yes I've done it before the Lexus alarm system once tripped disables the button by the leg even if the car comes open. You'll have to get in the car and unscrew the speaker in the rear and reach down into the trunk to retrieve your keys