Default [Q] Screen Protector to enhance touch sensitivity?

Hi, I have - or more specifically, my dad has - a rather uncommon problem (at least that I've noticed): Skin is too dry/hard/tough for most touchscreens.

--> tl;dr: Is there a screen protector/other thing that can enhance the screen touch sensitivity? <--

Long version:

I bought myself a Moto Defy some years ago (when it was released) and though I'd give it to my dad, who back then was using a Samsung Xcover non-smart phone. He needs a durable device, because there's too many "accidents" where the phone just lands *somewhere*. Anyway, he wanted a smartphone and I thought Defy would be a good choice. Alas, that didn't go well as it just refused to register his touch in any way, shape or form if he didn't lick his fingers beforehand. Yeah, weird. My SGS2 worked, but obviously that wasn't a phone for him. I ended up giving that Defy to my oldest child. After various tests, I bought a Galaxy XCover for him and it worked... adequately. Not brilliantly, and not always, but it worked. But as you know, the first XCover is a rather limited device, even for basic use. The memory on it is ridiculously small for today's applications, and it fills up with only Facebook + Whatsapp + Hangouts installed. So out the window it goes (well, not literally, dumbdumb ) finally, after serving faithfully for over two years. I bought him a XCover 2 (the newer/red version that has that nice rubbery back) and he likes it a lot more than the old one. Problem is, that screen is not as sensitive as in the first one (or some other reason, I don't know really) and it rarely registers his thumb at all and the rest of the fingers just barely. If he moistens his fingers before using the phone, there is no problem.

Also, I remember back when I bought my first HTC Desire (the original, AMOLED one) the screen was quite smooth and "glidy" and after I bought a ZAGG InvisibleSkin, the touch improved much. The skin gave it a liiiiitle more feel and "resistance" (not really, I just don't know the right word) and I felt like it was a much better user experience with that skin.

So, the question is: Is there a screen-overlay-thingy specifically engineered for this kind of application, or should I just buy a regular ZAGG skin for the device and hope it improves the touch? As he likes the phone and I can't figure out any other phones with features needed for him, I'm willing to pay for the overlay so it doesn't need to be the cheapest out there, and I'm not looking for those cheap ebay-chinese 10pcs-for-1 -screen protectors (that admittedly work for the purpose of protecting the screen, but they rarely improve the feel of the device...)

ps. I'm not averse to tinkering, so if there's a perfectly viable product, but for another device, I'm willing to go that route and modify it for the XCover 2, if it is indeed possible (obviously not possible for the tempered glass products, for example).
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Sony Xperia Z Ultra (Sony 4.3)
HTC One (HTC 4.3)
Apple iPhone 5 (iOS 7, Jailbroken)
Samsung Galaxy Tab 7.7 (Samsung 4.0.4)
Nokia Lumia 710 (Rataplan v5.0 WP7.8)
Apple iPad (iOS 7)
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Misc: Samsung Galaxy Tab, HTC Hero, XCover