Much as I like an electronic solution for things, sometimes it's more expedient to have a simpler, mechanical solution. The suggestion for a relay in the other USB thread would be ok
if a suitable relay could be found.
So, I've put this little assembly together, & done the unthinkable & actually tested it for a while reading. I used my forehead & then my mouth & both worked ok, but, apart from the usual aches & pains, I'm relatively able bodied so I've no idea of course if such an assembly is usable by your Dad (or anyone else needing an alternative page forward) but it might be worth a try?
The thin dual walled polycarbonate sheet underneath my Kindle is just to take up the space between the plastic bracket & K3 base so the bracket is a snug fit.
An additional right angled bracket could be attached adjacent to the hole over the "page back" switch, & the knitting needle, er, I mean "activating mechanism" pulled out & reinserted into the other bracket as necessary. I presume the "forward page" would be the most frequently used?
I borrowed one of my wife's knitting needles, & I really wanted to cut off the tapered end but it's the only size she has so I decided discretion was the better part of valour here
Hope this gives you some ideas.