Just a couple of suggestions...
I like the idea of changing reps often but honestly don't think dropping down from a 10 rep range to an 8 rep range is enough to matter. I would drop down to a 5 rep range.
Structure.. I would change to the following
WK 1: 2X15 30 seconds rest
WK 2-3: 3X10 60 seconds Rest
WK 4: 5X5 90 seconds Rest
Workout A
Flat Bench / Seated Rows, simi-supinated (palms facing)
Oh Press / Lat Pull downs, Supinated
Seated DB Shrugs / Side DB laterals
Workout B
Incline Bench / DB Rows (on an incline bench)
Arnald Press / Lat Pull Downs, Pronated
Seated Armpit shrugs / DB Front Raises
Workout C
Weighted Dips / Seated Cable rows Wide
DB OH Press / Lat pull downs, Supinated
Seated Shrugs / BO-Rear DB Laterals
On almost every workout you have both flat and incline bench and Oh press. I think that may be a little much on the pecs and delts. I would consider cutting it down.
I know you didn't want to include isolations but since your friend is limited to seated exercises.. that eliminates a lot of good lifts and in order to add a little variety and avoid hitting one mucle group with too much volume.. I've added a couple of Iso's to the mix.. Just an option