I would think that changing the parameters for the engine/drive train of the lift truck in any way would be a HUGE liability issue. Maybe adding a separate horn assy which only activated when the unit was running w/the seatbelt not engaged might be an option.

As far as wearing out starters- you are spot on. I had a national account which was very safety conscience & they began a program which required the forklift to be turned off every time the operator left the seat. Needles to say that starters & ring gears became a majority of the repairs I did. Unfortunately, from a safety standpoint, the program didn't last a year.