So I went ahead and bought myself a CBRPS SKSAR bullpup kit awhile back, assembled it and after some necessary tweaking finally got an end result that was reliable, easier to clean, and didn't throw the brass into my face. Long story, that whole adventure.
More importantly, among a few other reasons for choosing this kit over the Shernic were the bolt release button and the non-reciprocating charging handle on the left side. Very clever pieces, those. Today I got to thinking, these should both be doable on a conventional SKS without touching the receiver. The bolt release button could be a part of a receiver cover with extra material that goes along the rear of the bolt carrier. From there, it's a simple matter of having an identical style release that CBRPS uses - in my case it seems to work quite well. It seems to work 100% of the time if I give it a forward motion so I think the design would be improved upon by being at an angle similar to the forward assist on AR-pattern rifles.
The charging handle method used on the CBRPS design would be a little rougher to implement on a conventional SKS but should also be possible. I simply envision a Magwedge type rail with a slot so flat stock can be connected from the left side to the right side, with slots and bolts with washers for the flat metal stock can glide back and forth easily with a piece touching the charging handle on the bolt carrier. This would be spring assisted as to spring back to its starting position when used to charge the rifle. It's a bit harder to describe how this works without seeing it up close, but it's actually quite simple as is the bolt release.
Perhaps I can take some pictures of the kit and then present photoshop images of my own takes on how to accomplish the same things on a regular config SKS if there's any interest. Manufacturing of such parts similarly should be quite easy.