So, after doing some more research, I'm pretty sure there's no way to do this.
Fortunately, for most parts of the game (read: using special attacks in combat), the QTE's/Timing events are either fairly easy, or fairly inconsequential. The game just isn't hard enough that blocking every attack is the difference between winning and losing, and the difficulty slider is there if you really do have trouble.
Which leaves QTE's like the one that you're confronted with during the aforementioned night one Alien Abduction sequence. For which, at least for me, there was only solution which I could make work, after several hours of trying (and, I think, possibly damage to one of my two gamepads - something is seriously mistuned, and I suspect it is at least partly a bug, based on the lack of complaints about the issue at the level of severity I'm describing from console players). Either way, I settled on a solution because it worked, and because this is a single player game, and because my pride was already completely demolished. I cheated.
Specifically, I used Autohotkey and created a script that mashes the button required a dozen times instantly. I hit the macro once, and it passed the QTE check. You can literally follow the steps from the AHK Tutorial, and simply, instead of typing in #space::Run www.google.com
on the blank line, simply paste in
^!s::Send sssssssssssssssssssssssss
Then, whenever you press Control+alt+s, it'll act as though you've mashed the button. (S is the games keyboard equivalent to 'a' on the gamepad for these QTE's. Should you need a different button, just replace the s's with d's or a's or whatever.
Note: To use this macro, you'll need to unplug your gamepad momentarily so that the game reverts to keyboard controls, but the game switches between control schemes very gracefully and on the fly, so there should be no need to worry about restarting it or other hoops to jump through that might make this solution inconvenient.
This won't help with precision based QTE's, but for the truly egregious button mashers, this should solve the problem.
One easy way to tell, I've found, is by how your character holds the weapon when equipped. In the inventory screen, if the new kid extends his arm, resting the bottom of the weapon on the ground, it is two handed. If his arm is down and the weapon is held out at a nearly forty-five degree angle, it is one handed.
If there's any remaining doubt: equip the weapon, exit the menu, face the camera and look at how you are holding it. Two handed weapons will be held in both hands, while one handed weapons will only be held in a single hand, looking much like you do in the inventory screen.
Best Answer
If you are not holding the weapon that the strap-on is...well...strapped on to when you are attacked then no the perk will not take affect and reduce the damage. Just like how if you have a bonus fire strap-on on your ranged weapon the perk does not take affect when you use your melee weapon. I would suggest using that strap-on on what ever weapon you have out the majority of the time.