It seems like there are two primary ways to focus on a solution.
1) Modifying a machine for wheelchair based play (examples above)
- reducing the height by having shorter legs or having the machine on a lift system
- modifying the front of cabinet so a wheelchair can fit underneath comfortably
- possibly modifying the game so that alternate buttons can be used to flip
2) Providing tools or accessories or methods for a person in a wheelchair to play a "standard" pinball machine at any location. Issues needing resolution for this include getting the player to an appropriate
- height
- viewing angle
- position for using the flipper buttons (if possible)
or
- having some accessory to attach to the machine so the play can use "add-on" flipper buttons?
- and above all, maintaining safety while doing the above
My estimate from the OPs original post is that since his friend's dad is paralyzed from the waist down that if he could be "positioned" correctly and safely he'd be able to activate the standard flipper buttons... this makes me think something like a standing wheelchair could be used. [Though it may not make financial sense?]
See http://www.levo.ch/en/gallery/levo-lcev.html for an example of a "simple" version or search the rest of that site for other options.