Ok, so there are times when the solution to your problems comes to you in a most wonderful manner. Recently Szemi has been asking about how to use the 8x8 font characters. Now these are based on the standard ASCII table, probably to allow for ease of conversion from plain text files to game data. It skips Keen's internal keyboard mapping entirely.
While looking at them my brain flickered and said 'Hey wait a minute, in standard ASCII 'Y' is $59... that means...
So yes, this is far, FAR simpler than I thought! All you need to do is look up a character on the standard ASCII table which I have now added to the wiki at http://www.shikadi.net/keenwiki/Patch:Scancodes
It seems ctrl and alt, as 'control keys' cannot be used in this manner, the game refuses to accept them as valid input in this case. It does however accept enter, esc, tab and backspace and a little remapping would probably be of great value here.
I now have a complete understanding on how things like the savegame windows work (Inputs esc or 1-9) or the Yorp messages (Dismiss with 'enter') So any patches required to change their inputs are easy enough to generate.