Well, why not? If you put a 2nd switch in parallel to a 1st switch, both switches will act the same.
But that's theory.
If I understand your 'nearside door' correctly, you mean the door on the passenger side. Right?
So you'd need an additional switch to replace the blank on that door. Don't know id that exists in the same style. Otherwise it would need to be some generic switch and that won't look very nice.
And then wiring. You'd have to run a wire-pair from door to door. So to the inside of the door, through to the passenger compartment, through the dash and all out to the passenger door again. What a hassle!
Couldn't you just ask your passenger to ask you to push the existing button, if they want the doors open?
Or they could just operate the handle twice, to unlock it anyway.
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Edo
(2003 Silver 1.4 Tdi Exclusive(SE), black interior, sport seats, heated mirrors, JVC KD-SH909RB cd-receiver, Infinity Kappa 63.1 + Vifa on-dash tweeters, 12" Subwoofer on 300w Amp)